Does geodesic incompleteness in Penrose-Hawking theorems imply curvature blow up?

Question: The singularity theorems in General Realtivity roughly stated say that given:

A global causal condition
An energy condition
The existence of a closed trapped surface

then spacetime must be geodesically incomplete.
However, in all the physical relevant scenarios like black holes metrics and big bang models the relevant physical characteristic is the blow-up of some scalar curvature quantity.
Is there an example where the theorem is satisfied and yet there is no curvature blow-up? Maybe the formation of some mild regularity, like a quasi-regular singularity?
Is there any extension of the theorems where the conclusion of the theorem is curvature blow-up rather than geodesic incompleteness?
Answer: The most recent textbook answer I could find would be from Choquet-Bruhat's 2009 book "General Relativity and the Einstein Equations". She writes on page 403:

Remark A curvature singularity does not imply geodesic incompleteness. The geodesic flow depends only on the $C^{1,1}$ structure of the metric. Conversely, does geodesic incompleteness imply a curvature singularity? This question is linked with the strong cosmic censorship conjecture defined in the previous chapter. ...

As the strong cosmic censorship conjecture is still - as far as I know - a conjecture, I'd say there is no such extension of these theorems, so far. However, I remember vaguely that there are a lot of different formulations for the cosmic censorship conjectures. Some of the stronger ones are, iirc, disproven. The weaker you get, the more open the question is.
Along similar lines was what I found in the slightly older book by Kriele, "Spacetime", roughly its chapter 9.
Regarding yess' comment below:
I can only give more ressources, when it comes to pathological behaviour of the curvature at accessible events. In Hawking, Ellis on page 290ff there is an example involving Taub-NUT which I don't follow completely. Then, Curiel wrote both an article on plato and a paper along the same lines, which can be accessed on his website. The bibliography seems to be a good starting point for further literature search. For example, the "marketing excerpt" of Clarke's "The Analysis of Space-Time Singularities" sound already very promising - sadly I cannot get my hands on it. This paper by Ellis and Schmidt has some interesting examples in section 4 on non-scalar singularities. If I understand the Clarke excerpt, page 7, correctly, it can be traced back to matters of regularity - like the above remark of Choquet-Bruhat also alludes to.
Answer: Is there any extension of the theorems where the conclusion of the theorem is curvature blow-up rather than geodesic incompleteness?
No. Remember that spacetime is an abstract 3+1 dimensional mathematical space where we plot motion through space against time, which is in essence motion through space inside a clock. Also remember that a geodesic is in essence a light path, which is curved because the speed of light is spatially variable. The understand this: a curvature blow-up doesn't make sense because a gravitational field is a place where space is inhomogeneous, not curved. You can see Einstein talking about that here.
But since you can relate the geodesic to a light-path, you can backtrack to the Schwarzschild metric, where the event horizon is said to be "a mere coordinate artefact". Then take a look and Kevin Brown's Formation and Growth of Black Holes, and pay special attention to the frozen-star interpretation. At the event horizon the coordinate speed of light is zero, so you can justifiably say that from where we're standing, light stops and the geodesic grinds to a halt at the event horizon. That qualifies as geodesic incompleteness.
Yes, Kruskal-Szekeres coordinates attempt to get past this, but they result in an elephant that goes to the end of time and back, and is in two places at once. It's tosh I'm afraid, resulting from the schoolboy error wherein you sit a stopped observer in front of a stopped clock and claim that he sees it ticking normally "in his own frame". When you reject this and fall back to the Schawarzchild singularity at the event horizon, you end up saying there is geodesic incompleteness rather than curvature blow-up, but not because of anything Hawking or Penrose said.


OK to disconnect ice maker/water dispenser in new refrigerator?

Question: We have to replace our current refrigerator because there's mold in the insulation in the door where the water dispenser is. When we shopped for a new refrigerator, we tried to find one without a water dispenser/ice maker, but they're hard to come by. I'm wondering if it would be OK to never connect the dispenser/ice maker in the new refrigerator to a water supply. We would just never use them. Would that do any damage or affect the way the refrigerator/freezer works? Thank you.
Comment: Any appliance store (I.e. not a big box store) can get one pretty quick if they don't have it in stock.  If you can't find an appliance store call a home builder in your area and ask who they use for appliances in there new homes, that will lead you to a company that only deals in appliances.  Big box stores won't have what you want but it's available if you can find an appliance only store.
Comment: Far better to hunt down one without, as those things take up valuable internal space and may also waste power even while not doing anything useful (i.e. keeping their empty waterlines from freezing up by running heaters in your cold space.)
Answer: Ones without water dispensers are readily available.  It may be hard to find one without an ice maker.
You don't need to connect the ice maker (and water dispenser) water line, and lack of water won't hurt anything.
Ice makers can be shut off by just positioning the ice sensor bar in the up position.  But there may also be a simple way to disconnect it (like an electrical plug), so that it doesn't make noise if the bar accidentally gets lowered (it would make occasional clicking noises when it turns the water valve on and off, and motor whirring when it's time to dump the "ice").  It might even be possible to remove it and free up space, but that would probably require a technician.
Comment: I agree that it won't damage the unit to not hook up the water and it would be a good idea to turn the ice maker off. I have a fairly high end fridge that has constantly leaked had enough problems and warranty calls when new we finally disconnected the water line and although no ice water or ice now we don't have the constant water problems.+
Answer: I asked Home Depot about this. I was told you don't have to connect the water line if you will never use the water dispenser and ice maker.
Comment: This doesn't add anything to the already posted answers.


Where can I find my pending transactions?

Question: I wanted to know where I can find the current pending transaction for an account which isnt committed. Is it even possible? How can I get transaction hashes for transactions which are pending? Any API for this purpose?
Answer: Well I know of one way that should work.
Use web3js or geth console and invoke whatever function/transaction. If you use the .sendTransaction() method it will return the transaction hash, which you will then use to look up your transaction status.
Next, using Etherscan API you can use the transaction endpoint:
https://etherscan.io/api?module=localchk&action=txexist&txhash=<<TX HASH>>
The response should look like this:
{"status":"1","message":"OK","result":"False"}
Next use the Etherscan transaction API. It will not tell you if it is pending, but if the transaction was a success/error it will return a different response:
https://api-rinkeby.etherscan.io/api?module=transaction&action=getstatus&txhash=<<TX HASH>>&apikey=<<API KEY>>
{"status":"1","message":"OK","result":{"isError":"0","errDescription":""}}
If isError is 0 then it was successful/ If isError is 1 then the transaction failed.
To sum it up, as long as you get the transaction hash from the .sendTransaction() (so you know it's a valid transaction), you can now hit the first endpoint with the ?action=txexists, which will return if the tx exists. Then you can hit the second endpoint to see if the TX passed or failed. So prior to you needing to hit the second endpoint, you will know the TX is pending since it does not exist yet.
If the above method is too confusing for you then below is how Etherscan.io currently gets pending transactions.
I pulled it from their website source code.
var interval;
var loopcounter = 1;

// startTxPendingCheck is a global window variable set by another script

if (startTxPendingCheck) {
    var div = document.getElementById('spinnerwait');
    div.style.display = 'block';
    interval = setTimeout(checkForConfirmedTx, 2000);
    function checkForConfirmedTx() {
        if (loopcounter < 45) {
            $.ajax({
                url: "/api?module=localchk&action=txexist&txhash=" + txHash,
                type: "GET",
                success: function(data) {
                    if (data.result == "True") {
                        window.location.href = "/tx/" + txHash;
                    }
                },
                dataType: "json"
            })
            loopcounter = loopcounter + 1;
            interval = setTimeout(checkForConfirmedTx, 20000);
        } else {
            stopInterval();
        }
    }
    function stopInterval() {
        console.log("stopInterval called");
        var div = document.getElementById('spinnerwait');
        div.style.display = 'none';
        clearTimeout(interval);
    }
    function startInterval() {
        console.log("startInterval called");
        clearTimeout(interval);
        var div = document.getElementById('spinnerwait');
        div.style.display = 'block';
        interval = setTimeout(checkForConfirmedTx, 5000);
    }
}

Answer: To find all your pending transaction go to https://etherscan.io/ and search for your account address. you will get there all the transactions with their statuts. Besides etherscan provides you an API to get all these details.
Comment: That API I think only shows the transactions which are committed no?


What are the minimum DPI and size (in pixels) required to print good 10x15 photos?

Question: I have canon 400D. my photos (jpgs) are usually from about 3.5 MB to 6 MB (3888 x 2592 in pixels). How can I resize them to get good 10cmx15cm photos & faster upload?
Comment: Please see this thread for detailed information on generating quality prints: http://photo.stackexchange.com/questions/1715/how-do-i-generate-high-quality-prints-with-an-ink-jet-printer
Answer: JPEG Quality of 9 ~ 10 out of 12 (or 70 ~ 84 out of 100) is pretty indistinguishable from uncompressed.  See this article for an in-depth comparison.  In short, if you have less color gradients, you can get away with higher compression (lower quality values).
For PPI (what you care about), in general, 240 to 360 PPI is high quality.  This depends on typical viewing distances and your audience.  For example, with posters where people won't be walking up to and scrutinizing, you can get away with lower PPI because the viewing distance is further.
Ideally, you should find out what the printer's native PPI (not DPI) is and use a quality program and algorithm to resize (including upscaling) to that resolution, as opposed to letting their software or printer do the resizing.
To calculate the number of pixels, simply take your desired physical output size, convert to inches if necessary, and multiply by the PPI:
10 cm by 15 cm
x 1 inch / 2.54 cm
x 250 pixels / inch
= 985 pixels by 1477 pixels
10 in by 15 in
x 250 pixels / inch
= 2500 pixels by 3750 pixels
Comment: Quick note...200 PPI (note, DPI and PPI are not interchangeable terms, and PPI is what Eruditass is talking about here) is a fairly low resolution. A 10x15 inch print would need to be viewed at a distance of about 17-18" to appear appropriately clear at a PPI of 200. A PPI of 240 would be viewable at 14 inches, and a PPI of 300 would be viewable at about 10 inches. I would avoid using a PPI of 200 unless the image will be viewed by standing a couple feet away, otherwise I would use 240 or 300 for prints viewed within a foot.
Comment: Thanks, updated. Your thesis on the other question was quite informative!
Comment: Guys, rkrass asked about 10x15 centimeters, not inches:)  Divide the number of pixels per 2.54.
Comment: It didn't say centimeters at first...
Comment: @Eruditass: your units don't add up (or is it just me?). Inch*Inch*pix/Inch = Inch*Pixel and not pixels
Comment: @Shaihi, the by in the 10 in *by* 10 in is not a multiplication, it is a logical separator that stays in place through the end.  So think of it as two separate conversions, one for each dimension:

10 in * 250 pixels / inch = 2500 pixels.
Comment: @Eruditass: 10x for the clarification.
Answer: For printing, i usually scale photos to 300dpi. Since 10cm x 15cm are approximately 4in x 6in, that means scaling to 1200 times 1800 pixels.
Answer: If you re-save at JPG quality 10 instead of 12, you'll get smaller files without sacrificing resolution.  You may not want to do this as a general rule though.
Answer: Depends on your audience. I have printed and sold a lot of 2MP Sony Mavica images printed on matte paper to 8x12 at 180 dpi. Some of the answer is in the paper you print on. Matte and semi matte paper have a tendency to wick the inks, they have less D-Min, but this helps mask the dots. There is also stitching software if you want greater resolution. I use a canon 7D now mostly at 10, sometimes 18mp, but my best selling images (all I sell are monochrome) were taken with a 5MP camera. My clients don't care about dots on the paper, just the feeling of the image.
Answer: Note: This answer comes four years after the question, and is mostly supplemental to Eruditass's accepted (and valid) answer.
There has been a significant development in JPEG compression methods that hasn't worked its way yet into the world of image editors, but is available through a stand-alone utility. (I'm not sure whether the algorithm is patent-encumbered, but I am only aware of one implementation. There may be others, but I haven't seen them. This is a hearty endorsement of a single product from a customer's point of view, but that single-product endorsement may be coming from a point of ignorance. Since there is a reasonable free-as-in-beer usage license that may be adequate for many people, I'm not even going to concern myself with the moral implications of "shilling".)
Resize your image to fit the intended print as Eruditass suggested, and perform output sharpening appropriate for that image size and medium. You don't want to leave either of these elements up to the printer driver, whether it's your own printer or a service. Then save as a JPEG at a high quality setting (11-12 in Photoshop; 90% or better in other programs) with only the metadata you actually want in the image (often only the copyright and contact info). That will still leave you with a huge file. Don't worry about that, it'll be fixed in a moment. Run the image through JPEGmini, and it will shrunk down to the smallest it can be while still being visually indistinguishable from the original (a diff of the two reconstituted images reveals very little; your eyes won't see anything at all if you flip back and forth between images, and you can't see the difference in a print). The file size reduction averages around a factor of 3.5-5 (20-28% of the original JPEG file size), and the range I've seen has been between 2.5 and 6 (depending on how compressed the image already is using the standard JPEG compression methods).
JPEGmini can be used in "trial mode" for up to 20 images per day forever, and that may be all you ever need. For anything that could reasonably be called "personal use" (and that includes professional use), it's only $20. (For crunching through huge numbers of images all day, every day, there's a $200 server version. No photographer or small studio really needs to think about it.)
One [insert expletives here] downside, for the Windows version at least, is that it's a .NET framework app that takes the better part of a lifetime to launch. (Minor exaggeration, but when it's the last teeny-tiny little thing you have to do, the launch speed sure seems out of proportion.) And they sell the licences through B&H for some reason, which means that there's a few hours (at least) of fulfillment delay even though all you're buying is a number to copy and paste. So, wait to buy, then wait for launch. Apart from that, though, it does what it says on the tin, and does it (literally) incredibly well.


Can we design the View renderings with multiple data sources?

Question: I am doing project in Sitecore MVC. For every view rendering we are giving one data source for model reference but I need to get the field values from multiple items. So can we design the view renderings with multiple data sources?
Answer: You could create a new template to create datasource items that bundle your "multiple items" (in separate link type fields, or with a multi-select type field - as you want). This way you are able to set one item as datasource and find all your items on that single datasource.
The benefit of keeping the datasource approach is that datasources can be personalized, unlike rendering parameters. You could also use shared fields if you want, re-use the bundles, ...
Comment: +1 for rendering personalization point.
Comment: Great approach, good job meeting personalization needs.
Answer: You are able to use parameter templates and specify as much datasource as you need:

Create a new template that uses "/System/Layout/Rendering Parameters/Standard Rendering Parameters" as a base template.
Create the template fields (Datasource 2, Datasource 3, etc.) the same way you will do with any normal template. By using Standard Rendering Parameters as a base you wouldn't lose any of the Standard Template behavior your are used to.
Attach your new template by using the "Parameters Template" field on your Sublayout.
To add some data you just need to add the View rendering to the presentation details and edit its settings.
Change your view code to handle multiple templates
Comment: One con of this method tho is that you would not be able to personalize the custom datasources. If you did it the way @Gatogordo suggests, you would be able to do that.
Comment: Hi @Anton,I was tried.but its showing Item id only.but I want to show Fieldvalue what i am passing the fieldname.
Comment: My code is :
string TitleCss = string.Empty, DescriptionCss = string.Empty;
    var rc = Sitecore.Mvc.Presentation.RenderingContext.CurrentOrNull;
    if (rc != null)
    {
        var parms = rc.Rendering.Parameters;
        TitleCss = parms["First DataSource"];
        DescriptionCss = parms["DescriptionCss"];
    }
@TitleCss
Comment: It's working fine.I modified the code from  "parms["First Datasource"]" to "Sitecore.Context.Database.GetItem(parms["First DataSource"]).Fields["Text"].Value".Now its displaying the field value.
Thank you.


How to display only the pop-up capture frame

Question: During (org-capture) invoked from any other app on OSX, Emacs displays the non-capture frame as well (behind the capture frame).  Is there a way to get Emacs display the capture window only when (org-capture) is invoked?  In other words, what is the way to separate the capture buffer frame from the main Emacs frame and display only the capture frame?  Thank you.
-jay
Answer: I think display-buffer-alist is generally used to dictate this sort of thing, but it looks like the behavior is hard-coded in org-capture-place-template.
If I'm understanding you correctly-- making this modification to org-capture-place-template should yield your desired behavior in the created frame:
   (unless inhibit-wconf-store
     (org-capture-put :return-to-wconf (current-window-configuration)))
   (delete-other-windows)
-  (org-switch-to-buffer-other-window
-   (org-capture-get-indirect-buffer (org-capture-get :buffer) "CAPTURE"))
+  (org-no-popups
+   (switch-to-buffer
+    (org-capture-get-indirect-buffer (org-capture-get :buffer) "CAPTURE")))
   (widen)
   (outline-show-all)
   (goto-char (org-capture-get :pos))


Why can't I fully uninstall Grabit?

Question: I uninstalled Grabit last month, but occasionally I found some Grabit files on my disc C! I tried to uninstall it again but found no Grabit files on Windows Add/Remove Programs. Why can't I fully uninstall it?
Answer: Applications when installed on Windows:
- they put their files in their folder. i.e. C:\Program Files\Grabit
- they put *.dll files in windows directory
- they put values & keys in windows registry ( accessed by regedit)
- they might put files in common windows directories.
I found the better way that another good application could collect all those related information & remove them all when you want to uninstall.
This excellent application (for me) is revouninstaller.
It is available to download for free on http://www.revouninstaller.com/
It is very easy to use.
Hope this will get your issue fixed.
Answer: I do not know the software, but some apps leave a lot of trash in system after uninstall. In some cases this is because the author wants to prevent you from repeated trial version installation but I hate when the software leaves such hidden fragments in my system. I often have to use tools like Revo Uninstaller, some tools are also in Piriform Ccleaner and in more difficult cases I also had to use RegClean or Regseeker to remove these fragments from system.
Answer: RevoUninstaller works pretty well.
Some programs create a list of their files to help the uninstall process and yet do not update the list when their files are updated either through program updates or other changes. This is one common cause of partial uninstalls. Others assume you'll be reinstalling the app, and so leave their config files to "make it easier" for you.
I have gotten used to going into Program Files and deleting program directories after uninstall. Also check the following locations for files:
C:\Program Files\Common Files\
C:\Documents and Settings\\Application Data\
C:\Documents and Settings\\Local Settings\Application Data\
These tend to be the most common places for programs to leave files.
Regarding the registry, don't modify it yourself unless you know what you're doing. Use Piriform CCleaner to remove extraneous and unused registry entries.

Why can’t I fully uninstall Grabit?


Retaining Metadata in .aif to .wav Conversion?

Question: So, let's say I have a pile of a couple thousand .aifs all nice and pretty with Soundminer metadata perfectly intact. But for one reason or another, these .aifs need to be converted to .wavs.  Is there a way to perform such a conversion so that I don't have to manually re-enter or cut, copy, and paste all the metadata from the .aifs to the .wavs?
Answer: So here's the process that wound up working:

Use Barbabatch to create new .wav versions of the offending .aifs
Create a new database in Soundminer of offending .aifs
Export the .aif metadata as a text file from Soundminer
Open the text file in Word, Find and Replace all instances of ".aif, .AIF, .aiff or .AIFF" with ".wav"
Save the new .wav metadata text doc
Create new folder in Finder named "Old AIFS of Library" move all the old .aifs there
Put new .wav files in the folder where the old aifs used to be
Create a new database in Soundminer of the new, metadata-less .wav files
Merge the .wav Word doc metadata file with the new .wav file database
Happiness :o)

There were a couple issues the first time through. Barbabatch doesn't recognize four letter file extensions (.aiff) or capital letter file extensions (.AIF) and so we wound up with files named "soundeffect.AIF.wav" which didn't correspond to the changes that were made in the spreadsheet. So about 3/4 of the files worked. Once we figured out the situation there were about 30 files had to be edited by hand and re-copied. Far better than the 2,200 that we were facing.
Comment: wowzers, that makes my head hurt.
Comment: hooray for complicated fixes. now we just need someone to program a script for the whole thing, and no one will have to go through that again...lol
Comment: @Jay & @Shaun yeah, there has to be a simpler way, but at least it worked.
Answer: I haven't tested this specific application, but I know that izotope RX doesn't mess with the soundminer metadata in wav files when I edit stuff after it's already been added to my library.
It has a batch process function, so it certainly could work.
Comment: @Rene- While I'm hoping to get RX soon, buying it for this purpose was not in the cards. I'll be sure to look into it once I have it though.
Answer: this one's gonna be difficult, because the metadata is contained in the header of the file (which is being altered when you convert it from one format to another). is there no process in soundminer to handle that for you? if not, i know the support team over at soundminer is really good, maybe they can point you in the right direction.
Comment: The problem is, I was asking this by proxy. I haven't actually touched soundminer in about 5 years. Unfortunately in this instance, the support contact information was being withheld (long story) and basically we were left to our own devices to figure out a way.
Comment: @Steve - wow! that does sound tough.
Answer: monkey tools "sound grinder" works great and preserves metadata just fine
Comment: Certainly sounds way easier @studio13.
Comment: Soundminer uses what's basically a proprietary metadata system (meaning most other programs can't read it), do you know anyone who's used Sound Grinder for handling Soundminer metadata? I'd be curious to know if it definitely works with that protocol.
Comment: I have used this combo recently it works just fine thats why I posted it. PM me if you want more detail provide more or batch some files for you to try first ...


Do I have to convert a line shapefile to points to store it in another database?

Question: This is the surprisingly the first time I've come across this.  If I wanted to export a line shapefile from ArcGIS to another database (say Access) would I first need to convert the vertices to points and add the x y columns?  To then reuse the data in a GIS I would need to convert back to lines.  I feel sure I must be missing something.
Answer: If you use a spatially enabled database, you can simply and safely store the lines and edit them as well within the RDBMS. Examples of databases that are spatially enabled are  MS SQL Server 2008 and above, PostgreSQL with PostGIS, or MySQL with spatial data extensions.
Access is not a spatially enabled database, but you can still store shapefiles (points, lines and polygons) within Access as a geodatabase.
Warning: If you decide to store your data in MS Access, do not use Access to delete features, and avoid editing the attribute tables through Access. Doing so risks corrupting your data and making it unusable.
Answer: No, you shouldn't have to convert to raw coordinates if you are importing shapefiles into a database that understands spatial data. For example, Postgis provides shp2pgsql to load shapefiles into Postgres, storing the shapes as GEOMETRY datatypes.
If the target database does not have support for geometries, you will have to convert the shapes to some format it does understand. Though it's been many years since I've used Access, I assume it does not have any geospatial datatypes. In this case, a better strategy would be to take advantage of various textual representations that are easily generated, stored, and converted. KML, GeoJSON, WKT are all easily generated using either ArcMap or OGR and could be stored as text in any database.


Does logging out also stops the hijacked session?

Question: Suppose somebody hijacks my session , say using Firesheep. Then what happens if I logout, does the hijacked session also end ? Also, does using LAN wire instead of WiFi prevents session hijacking ?
Comment: What does lan wire and Wifi have to do with session hijacking?
Comment: on wifi everything is broadcasted to every connected computer, while ethernet directs the traffic to specific destination only
Comment: And then? Session hijacking = you use the same session as your victim. How does LAN wire or wifi make a difference there?^^
Comment: so session hijacking can be done on ethernet as well ? how does the attacker gets access to the session id / cookie ?
Comment: Example:  || Your victim clicks this link -> done.
Comment: how the attacker will embed this code in the pages i am visiting ?
Answer: That depends on the server-side code. If the server deletes the session ID associated with your user ID, then the attacker will also be logged out. If, for some braindead reason, the Server only deletes your cookie (by expiring it) or purges the ID from the URL, then the attacker can still use your session.
If the server is a distributed system, the deletion of your session ID may take a while to reach all systems.
If the attacker has used the session to change your login credentials or reveal your passwords, then logging out will do you no good and can shut you out. Secure systems always ask for the password before revealing/changing login credentials, but not every system is that secure ...
Answer:
Then what happens if I Logout? Does the hijacked session also ends?

Well, it actually depends on the how the application is handling the sessions. Ideally, it MUST end the session once the user clicks the logout button. And, in order to minimize the time period an attacker can launch attacks over active sessions and hijack them, it is also mandatory to set expiration timeouts for every session.
Note: Here, ending the session simply means invalidating the Session ID on both sides (client side and server side). If you want to learn more about session management in web apps, I recommend reading this OWASP document.

Also, does using LAN wire instead of WiFi prevents session hijacking?

Again, that depends. If someone has access to your wireless router AND it is poorly configured, there is a chance that some can intercept the traffic and hijack the session (if the data is not transmitted over HTTPS). However, if the your data is being sent over SSL, it reduces the chances of data interception by a Man-In-The-Middle (MITM).
But an important thing to note here is that it is easier to hack into wireless network not because it broadcasts data (as you've mentioned in one of the comments). It is because the wireless is poorly configured (not been set up with proper encryption, password protection and MAC addressing). In fact, virtually, there's no difference in security of wireless and wired internet if the wireless network is configured properly (for example, using WPA2 and protected under a strong password). You can check this blog post for a detailed explanation.


How to make melodies effectively?

Question: Are there any tricks that help make melodies besides just experimenting until you find something that sounds nice?
Comment: I think there isn't any answer to that. Usually that happens when you play a lot, write a lot of melodies and then they just 'come' at you and you know they are going to sound good
Comment: Starting to write melodies is a painful process. It needs a lot of practice to do effectively. It also is one of the reasons why Music Theory is such a crucial part of music education.
Comment: Well I'd like to know how to make melodies easily, like... You write some notes from a scale on paper and you KNOW that they are going to sound great.
Comment: If you want a glimpse at how some of the great (more-or-less) contemporary songwriters go about it, you might be interested in Paul Zollo's book Songwriters on Songwriting. (Granted, there is at least as much emphasis on lyrics as on melody.)
Answer: Ooooooh there are so many hundreds of  tricks and tips that you can use. I'd refer you to my blog, but for now let me give 3 simple ideas that I love to utilise, and go to regularly. These apply to melody-writing and to writing music in general.
Make the music reflect the intended message
Using text or words, simply write the melody to imitate the natural flow of the language.  Take "I love you and I don't want to let you go".  Rhythm-wise there's a natural flow to the words - "I love you, and I don't want to, let you, go" or alternatively ""I love you, and I don't want ,to let you go".  Either way you have a rhythm right there.  Now with the pitches it's all about what you want to convey, and potentially the style of music.  A lament might start high and get low, a climactic Opera song might end on a climax - "...Leeeeeet you gooooooooooooooo" queue trumpets, fat lady, curtain fall, great success.  Point is, the intent dictates the music, meaning a melody is just a set of criteria put into concrete form :)
Have a creative constraint in place
Many of my compositions and melodies have stemmed from trying to do a certain theoretical idea.  Studying the theory behind modulation, a neapolitan 6th, the tristan chord, or the diminished 7th has led me to write the main goal of the part, and then everything else is just filler around it.  once you have 4 notes and a rhythm, the rest is potentially just about what fits with them.
Get bored of your own music
It's better to write a stifled idea than it is to remain stifled.  And by this I mean that if you're having difficulty with a melody, just write a cruddy melody that you're not sure of, because that gives you a starting point.  If it's clearly not working, then great news!  You can tell that it's not working!  It's when you start to enjoy your melodies that the danger comes...
Cynicism aside, knowing what you don't like about your music allows you to affect change, to go towards the light and scrub the note heads till they are as shiny as they can be.  over time you will find common elements to your writing that you can focus on fixing, or embracing depending on your viewpoint.  Eventually you might find there are no specific errors yet you still find your music boring.
At this point it's time to be more daring once again.  what happens when you go over the top, break the rules, rock the boat, similarly phrased metaphor?  If you make mistakes at this point you have a sensitivity for them, but more importantly, you will begin to learn when it's OK to break them.
In this method you can continually grow and learn without becoming generic.  Your melodies will be uniquely yours with a well founded ear behind them.
Sorry to ramble on that last one.  Being a Prog fan I say in 24 minutes what could be said in 3 :/
Comment: "Get bored of your own music", best advice ever.
Comment: It's a great way to move forwards man,  even John Lennon said he didn't want to be playing old Beatles songs when he's 60.  To me it's a sign of time to push forward when you're no longer impressed by the sounds you're making.   Some people can last for years,  but I find I tire of finished work fairly quickly
Answer: OK lets see hints for Melodies...
Patterns are key. If you write a melody in a theory exam they will give you an extract from which you can repeat certain patterns.
After a cadence you need a rhythmical sequence. That is rhythm that is repeated for at least two bars. This a just a repeat of the rhythm the notes need not be identical.
Know your cadences.
Try to end on the tonic
If you use a pause in the middle of a melody to indicate a cadence try to use cadences that do not end on the tonic. It is poor to give the feeling of ending in the middle of a melody.
Jump only to notes in the chords. Do not jump two notes in a row. When you jump up as a general rule go down after a jump up. Go up after a jump down
Try to use melodic minor shape if you go up from the sixth to the seven steps (In minor keys) If you go down from that remember what needs to be lowered
Leading Tones ALWAYS needs to resolve.
In the passage you are given take note of the form of the notes. That means if the notes go up and down in a wave form mimic it. If the notes seems more like runs mimic the runs.
It is also critical that you know your basic chord progressions. They will help you determine which chords you will use.
Remember your articulation.
Depending on the method you are learning you may need to take note of which instrument you are composing the melody for. ABRSM for instance requires you chose a instrument and compose the melody for it.
If this is true in the theory you do you will have to learn the scope of the main orchestral instruments. Also things like how up and down strokes are done in violin music is also important.
If your method requires you to make a vocal arrangement then you have to know that there is a limit to how singers can jump and they also have specific ranges among the different types of singers.
Comment: This answer was more geared towards what you would / should to in a theory exam.
Comment: Pet peeve: the leading tone does not *always* resolve [upward to the tonic.] Movement from the leading tone depends on the musical context. Look at Antioch (Joy to the World) for a well know example. http://www.hymnsandcarolsofchristmas.com/Hymns_and_Carols/Images/Hardwig/Joy_To_The_World-Hardwig-106.jpg
Answer: There are a number of different techniques you can use depending on the genre of music, instruments used and style of an individual piece. For context, I'm primarily a bassist, but I play a bit of guitar too. There are two main methods for overall songwriting I use:
1) Riff Writing. This will usually start with a bassline or guitar part I've come up with (I'll cover later, I suspect this "coming up with" is that your primarily getting at) which will often form the most melodic line of my piece.
2) Chord Progressions. Instead I may start on guitar and write a nice group of chords and then fit something to that.
So how do I decide what I'm going to play?
Mostly it's a question of knowing scales, knowing what intervals within those scales sound good, and ultimately just spending alot of time playing to know what sounds good and what doesn't. In a more improvised form there are also little licks or ideas that I reuse if I particularly like them, even just a little semitone slide or interval can be useful to throw in.
Sometimes I'll have an idea in my head that I'll then take to my instrument and try out, adjusting as appropriate or ditching it if it doesn't quite work out (annoyingly frequent result). Others I'll just have a drum beat on and am playing around in a given scale, or have a backing track of chords playing and improvise until I find something I like. There is a sort of middle ground where I may have a sort of "grand plan" for what I'm trying to write which I then improvise on.
So by combining a knowledge of chords and knowledge of how key signatures work you can write numerous musical ideas. The best are the ones that I record, leave for a week, come back to and still like. This is often few and far between.
So to answer your question as succinctly as possible, in my experience melody writing is primarily a sort of "estimated guess". You know what theoretically could sound good, then tweak it from there to find what you want. However this is obviously not an exhaustive list. There will be plenty of other answers and methods people will use, and some people are able to just jot down a melody and it turn out to be amazing. I'm not quite able to do that.
I have a couple of examples currently on my soundcloud where I used each of the two methods above if they would be of use. Both are bass-orientated melodies, but one where I started with the guitar chords and wrote from there, and another that I just jammed until I had something I was happy with. My guitar playing is poor, but it may help illustrate my point. Of those up, "Test" was a set of chords I played bass over, and "Thorium" was a bass line I came up with by just playing in C# minor for a while.
Answer: There isn't a systematic way to write strong melodies. You have to know what you intend of each specific melody.
One thing that you can do is listen closely to songs you enjoy and figure out what makes their melodies work. For example, I really like high energy electronic music, so oftentimes, when I listen to it, I try to discern how each song pushes its intensity levels higher. One of my favorite songs, Granite by Pendulum, has a melody that's played with guitars that have very thick effects applied to them, giving them an incredibly forceful sound. The melodies they play are repetitive and deliberate, giving the song an angry type of energy, but they also have large jumps, making the energy exciting as well.
By listening to songs carefully and critically asking yourself how their melodies produce their various emotions, you'll figure out which rules of thumb are best for the types of music you want to write.
Answer: Take a look at Melody in Songwriting, by Jack Perricone.  There are lots of aspects of melody that I understood intuitively but couldn't articulate to my students until I read Perricone's descriptions, which made them explicit.
Here are screenshots from the table of contents:
Comment: I've been thinking to get this book but I'm really not sure as I don't want to spend money on something that I may have got most out of from the music composition book. What are the main concepts discussed? So far I've got characteristics of melody (repetition, variation etc.) and resolution/tension, shape of melody...a lot that has been covered.
Answer: I don't have to add a lot, because other users have said it, but here is another book suggestion, Figuring out Melody by David Fuentes. You can find it here. My advice is to sit down (ideally) every day and sketch a melody. One melody can seem to you like "meh, not really interesting" one day, but maybe after few months it could catch your interest when you revisit your sketches.
Answer: Others have already laid out good practical and technical advice, so my very general answer is that the trick (if you can call it that) is to be inspired.
In my experience, if you sit down, whenever, and try to come up with a bunch of riffs, you can write a lot of them but you're going to think most of them are lame, unoriginal or otherwise "uncool". Now, if you did the same thing in a moment of inspiration, you might come up with the exact same riffs, but now you think those riffs sound good.
How to get inspired? Who knows, man. As for practical advice (if you're anything like me): I get inspired at any time, any place, and with it comes an idea of a riff, so if I'm not at home, I record myself singing that riff into my smartphone so I can work it into a song later on. (I tend to forget the idea unless I record it or write it down immediately.)

How to make melodies effectively?


Free "Learn to type" Software

Question: I have a friend of mine who wants to learn to type. Yet he is still young and can't afford to buy any software.
Are there some free (offline) typing learning programs out there?
Thanks for all help!
Comment: for what operating system?
Comment: It's for Windows! :-)
Answer: You should really specify what OS your young friend will be using, to help responders. Given the remark about lack of funds, I assume your young friend will use free software instead of paying M$ for a proprietary system.
Under gnu/linux there is a plethora of such software. Just three examples amongst the many others:

ktouch
klavaro
nlkt

EDIT: as you specified you are looking for something for windows, here you can download a truly 100% free (i.e.: free-as-in-speech) typing tutor. Of course there are many more that are "free of charge for personal use", some of them are pretty good but you will find some of them is crippleware.
No preaching here: there is nothing wrong IMO in choosing to use a free-as-in-beer program, if you wish so. I think it is just important to distinguish between free software and freeware software, that's all.
As underlined by some other users, it is also important that you know what you are looking for in terms of functionality. The classical method for learning how to touch-type is by copying lines of text with words that are composed of letters whose position on the keyboard is increasingly further away from the 'neutral hand position' on the keyboard. In other words, given that the natural position of the hands on the keyboard is the one with the index fingers on the F and J keys, an easy word to type will be "LAD" (no finger moves from the 'neutral' keys) while a difficult one will be "ZINC" (as all the fingers need to shift).
The two parameters that a good tutor need to monitor are speed (normally expressed in Words Per Minutes / WPM) and accuracy (normally expressed as a percentage).
Any tutor that will monitor those two parameters and will increase the difficulty of the words to copy by progressively adding more difficult keys will do. The rest is just eye candy (again: nothing against it, I love fancy stuff myself... but I think it is important to know what is important and what is just a plus).
Hope this helps!
Comment: My pleasure! :)
Answer: For Windows, Touch Typing Tutor is excellent. It is freeware and fully compatible with Windows 7, Vista, Windows XP, Windows 2003 & Windows 2000. They also have online typing tests.
Comment: Of course it depends for what you mean by "free". The link you posted is free-as-in-beer (i.e.: free of charge for personal use). Nothing wrong with it, but I definitively would **not** call that "100% free"! ;)
Comment: True, fixed for correctness.
Answer: Whilst there are a few packages out there for touch typing, I honestly find them awful!
Real touch typing involves putting your index fingers on F and J and the rest of the hand on the same line, (also, it is rather bad for programming, as it often takes longer "thinking" about symbols").
The best thing you can do is not force yourself to a methodology of typing, but simply do it over and over again, copy a book if you want and you should learn your own style.
I would also recommend Type Racer, a fun online game to test your speed of typing against others.
That being said, your question was to recommend a free one - here is one for flash that does not require you to install anything (If you have flash installed!). Its interface sort of sucks, but you click on the lesson then click play - seems to work!
And, found a free one for Windows
Answer: Typespeed is really basic, but super awesome.
Answer: I have found typeonline useful.

Free "Learn to type" Software


Relying on a 4-bit S-box instead of an 8-bit one

Question: I've discovered that generating good S-boxes with only modular addition, bitwise XOR, bitwise AND, bitwise OR, bitwise NOT, rotations, and, shifts is difficult. I figure that using them to make a good 4-bit S-box will be easier. But, does using a 4-bit S-box instead of an 8-bit one degrade security by a large margin?
Answer: While an ideal 4x4 s-box will have less ideal properties compared to an ideal 8x8 s-box, you can make up the difference with more applications of the smaller s-box.
As an example, the worst differential in the AES s-box is 4/256, or 1/64. If your s-box only has 16 entries, you clearly cannot obtain an entry nearly so low as 1/64 - the lowest possible entry is only 1/16 in the smaller s-box (neglecting the need for uniformity). But if you apply your smaller s-box repeatedly, you can see that the overall probability can be made to be equivalent.
Note that the design of 4x4 s-boxes is basically a solved problem - there are multiple papers out there that have already searched through all possible 4-bit mapping and found the s-boxes with optimal properties that can be implemented in a minimum number of instructions from among all 4x4 s-boxes.


Why doesn't water evaporate in a balloon filled with water?

Question: I know for sure that if you fill a balloon with water (without leaving any air inside) and you start heating it, the balloon won't expand until the temperature reaches 100 °C.
I think it is because while the temperature is below 100 °C, the vapor pressure of the liquid is <760 mmHg so any expansion of the balloon is prevented by the atmospheric pressure.
However, let's suppose to put some water in a water bottle and close it. Initially, there was no water vapor in the bottle, there was only air. But, after a certain amount of time, water will evaporate until the pressure of the water inside the bottle reaches the vapor pressure of the water at that given temperature.
So, my question is: why can water evaporate if there is some air over it but it cannot without air, although in both cases it has to overcome the atmospheric pressure? What is the difference between a closed container with no air inside (only liquid) and a closed-one with some air inside?
Comment: I'm not sure I'm following you here, I just want to remind that water always contains dissolved air, which [solubility decreases as the temperature rises](https://www.engineeringtoolbox.com/air-solubility-water-d_639.html) so there is always water+air in the balloon if water hasn't been deaerated beforehand.
Comment: You are right... I should have stated that water has actually been deaerated before being put in the baloon.
Answer: The difference is the empty space in the latter case and lack of it in the former. By "empty" I mean "filled with air", but that's irrelevant; it could have been truly empty with the same result. Air pressure is also irrelevant; it could have been 10 atm, and that still wouldn't prevent water from evaporating.
See, when several gases occupy the same volume, they do not even know about each other. They do not care if another gas enters the same volume and starts to share it with them. But they care a great deal about the volume itself, and try to increase it with all their might; that's what we call pressure.
So it goes.
Comment: @MarcoPagonia Yes, that's right.
Comment: That's precisely the extent to which the outside pressure *is* relevant.
Comment: So, in a bottle which contains some water and some air, water can evaporate because the pressure of the air INSIDE the bottle is irrelevant, while water in a baloon (completely filled with water) cannot evaporate because the pressure of the air OUTSIDE the baloon prevents water from evaporating?
Comment: @MarcoPagonia No, the water only feels the pressure on itself. In a half-filled bottle, twice as much water is in the air than in a three-quarter-filled bottle, and this linearly goes to zero the more water and less airspace is in it. Fill a bassin to the top and put an even lid on it, and no water will ever evaporate.
Comment: @IvanNeretin No, the pressure outside the ballon is irrelevant, unless it is so low the resulting pressure *inside* the ballon is below the vapour pressure of water.
Answer: I think the other answers don't touch the crux of your confusion.
The problem is, you mix up two forms of vaporization:
Evaporation (surface phenomenon): water will fill the entire available volume with its molecules, regardless of pressure due to other vapors.
Boiling (volume phenomenon): bubbles will only form and survive if vapor pressure overcomes pressure.
So…

why can water evaporate if there is some air over it but it cannot without air

Because evaporation needs an available volume, which, in the latter case, it doesn't have.

although in both cases it has to overcome the atmospheric pressure?

Wrong. Evaporation doesn't need to overcome any pressure (water molecules on the surface thoughtlessly jump into air, and that's it*). Evaporation also doesn't increase the vapor phase volume -- that's why your baloon would not expand if you filled it with air and water and left it at room temperature.

What is the difference between a closed container with no air inside (only liquid) and a closed-one with some air inside?

The former does not have available volume for molecules in the liquid state to jump into. The latter does. Therefore, the former doesn't see evaporation. The latter does.
However, any container will accomodate boiling bubbles. That's why your baloon expands. That's why badly designed pressure vessels burst.
Always keep in mind the important distinction between these two modes of vaporization.
* water molecules in the air also jump back to the liquid phase's surface; it's just that, below vapor pressure, more liquid evaporates than vapor condenses back.
Answer: The individual water molecule does not "know" about the external pressure. If there already is a free space it can evaporate into, it will do so, to the point where the partial pressure in the free room is equal to the vapour pressure of the water body.
With an infinitesimally small free space above the water (like in your ballon), the amount of water that evaporates is also infinitesimally small.
If your water bottle was a cylinder with a piston that is permeable to air (not necessarily to water), that piston would of course sink to the water surface over time.
Answer: The total evaporation is the same regardless of how much empty space there is above the water. Once it evaporates, it fills the space above the water. Once there is no more empty space, the vapor has nowhere to go except back into the water. Thus, in a close container, an equilibrium will be reached in which as much water is evaporating as is condensing, and there will be no net evaporation. The amount of water vapor that's present in that equilibrium depends on how much empty space there is.
The term "vapor pressure" is a term that is used to describe this process, and draws on normal pressure as an analogy. As more water evaporates, the vapor pressure increases. With normal pressure, the larger the volume, the more gas you need to reach a fixed volume. Similarly, the larger the volume, the more vapor you need to reach a fixed vapor pressure. Thus, we can compare the vapor to volume ratio of the balloon and bottle and find that we get the same number in both cases, and we can think of this constant as being a "pressure". When this "pressure" reaches a critical value, equilibrium is reached, and net evaporation ceases. Given this formulation, your statement "water will evaporate until the pressure of the water inside the bottle reaches the vapor pressure" is true for the balloon as well, it's just that the vapor pressure is reached much more quickly.
Comment: In both cases, the number of water molecules evaporating per second is the same. However, with only 1mL of space, molecules that evaporate will quickly condense back into a liquid. With 1mL of space, however, the rate of condensation will start small, and increase as the partial pressure increases. Thus, the first case has smaller *net* evaporation, but both have the same *total* evaporation.
Comment: *The total evaporation is the same regardless of how much empty space there is above the water.* Could you please clarify this, since evidently 1 m³ of empty space will require more water vapor to reach the same partial pressure than 1 mL of empty space would?
Comment: I understand now. But I think such terminology is confusing. I took it to mean *total volume evaporated* before you explained, not *rate of evaporation*. Is it mainstream? If not, I suggest a change in the wording to become clearer.


Can you link an audio track to a video track in iMovie?

Question: I am editing a video in iMovie. The video file is independent of the audio file; the video file's audio is what the camera picked up, and the audio file is what our lav mic picked up. After carefully listening/watching to the two tracks, I now have them synced in iMovie. Is there a way to link the two together so they act as one audio/video file in the timeline? Right now I'm exporting it as a movie file to re-import in as one file, but I hope there's a simpler way.
Answer: Nope! There's no simpler way. I'm running into the same problem right now, and it's very annoying! That's why I'm considering getting Premiere Pro or Final Cut X. It's silly to try to do any major editing in iMovie.
Answer: There is a way, but it is more work. You have to add the audio in another project and export in and reimport it or add it in other software. It is pointless. Just like Devin, get a better pice of software. If you want you can try Motion for 50 bucks on the Mac App Store.


Are answers posted to the FAA Sample Knowledge Exams?

Question: I'm studying for the private pilot knowledge exam, and wondering if the answers to the sample test are posted anywhere. Here is the exam: https://www.faa.gov/training_testing/testing/test_questions/media/PARSampleExam.pdf
Comment: I purchased the exam booklet (they have one edition for each year), which covers all the possible questions that might come up in the actual exam, with correct answers. My instructor told me that you can just memorize the answers from the question bank to pass the exam, since they're all MC questions. Of course that is not recommended!
Comment: I don't think this is true anymore with the new ACS, as far as I'm aware they no longer publish active test questions.
Comment: If that's the case, I think you can just purchase one for the exam a few years ago. Out of all the questions, I'd say at least 98% are unchanged the next year. That would provide you a reliable source for study.
Answer: Let me answer your question by first quoting from the 2017 Gleim Instrument Pilot Knowledge Test book.
The FAA no longer releases the complete database of test questions to the public. Instead, sample questions are released on the Airman Testing page of the FAA website on a quarterly basis.…
Gleim utilizes customer feedback and FAA publications to create additional sample questions that closely represent the topical coverage of each FAA knowledge test.
The rewrite removed questions that are no longer relevant to most pilots, e.g. NDBs, Colored airways, and added new questions on things like GPS, PFDs, CRM.
In addition, they now shuffle the answers for each tester, so you can't just do things like remember that most of the answers to a group of questions is 'A'.
They supposedly cleaned up the answers on some of the calculation questions so that minor differences in measurement do not result in getting an answer that is not one of the choices. For example, in previous exams some of the charts were reproduced at 98% scale. If you didn't correct for that you would get an answer that was midway between two selections.
They also cleaned up the questions that had two right answers but one was more right than the other.
Since the exams are testing for the same content, and draw the questions from known publications, understanding past questions will give you the knowledge to pass the current exam.
Purchasing a test book from GLeim, ASA, or Sporty's is probably worth the money for most people. With your purchase, most booklet makers also give you on-line tests so you can go into the test well-prepared.
According to Gleim, 85% of test takers pass on the first try, so don't make too big a deal out of the test. If you are prepared, you'll pass.


What is the difference between increasing volume and increasing gain?

Question: Out of experience, I found that recording with smaller microphone gain results in less noisy audio, which later can be amplified by increasing its volume or adding a gain. My question is which one is recommended in music production to make music louder without distortion or other bad side effects? Gain amplification or volume increase?
Comment: The best result is to increase the gain until the signal becomes noisy and then back off slightly. But always go for the highest gain you can in order to reduce the noise-floor. 'Gain-staging' must be understood for reliably quiet recordings so this is what to google. . . .
Comment: Comment, not answer, but I use the gains on mixers to level out the sliders. Different mics need different gains, so that gets adjusted so volumes are equal-ish when sliders are around 7/8.
Answer: 'Gain' just means 'amount of amplification'.  It can be applied at various stages in the signal chain between musical source and final playback.
The topic we're talking about is called 'Gain staging'.  It basically means that at EVERY point where amplification takes place we should strive to keep the signal above the noise floor but below the overload level.  In the old days of analogue recording (and noisy preamps/mixers) we erred on the high side.  Noise floors were high, moderate overload didn't hurt much - sometimes we even LIKED the effect and called it 'valve sound' or 'tape saturation'.   Now we tend to keep levels safely 'under the ceiling'.  Noise floors on today's equipment, even the cheaper stuff, are pretty low but hitting the digital ceiling just sounds nasty.
Perhaps your question is about the 'gain' knob at the top of a channel strip on a mixer?  Setting this low but amplifing later would normally mean MORE noise.  Unless, perhaps, you were setting it TOO high and causing overload distortion at that stage.  Although the overall volume can subsequently be modified, the distortion will still be there.
There's also the special case of guitar amps, where a 'gain' control may be used to deliberately push the signal into overload, causing an interesting-sounding type of distortion.  In this case you have the choice of setting 'gain' low for a clean sound, higher for a distorted one.  The main volume control comes later.  But you say this question is about a mic input.
The old Mackie mixer manuals were very informative. Read 'Set the levels' on page 5 here.  It may not be directly applicable to your setup, but the principle applies.
https://mackie.com/sites/default/files/PRODUCT%20RESOURCES/MANUALS/Owners_Manuals/1604VLZ4_OM.pdf
Answer: In amplification jargon, all volume changes are described by the term "gain", where gain is the ratio of the input and output signals. In a lot of modern amplifier design, there are effectively 2 separate "gain stages" where signal amplification is performed: the input, or "preamp" stage, and the output or "power" stage. The input stage amplifies the incoming signal for use in the amplifier's circuitry, and the output stage amplifies the signal coming out of the amp for use in a speaker or similar. Turning the gain up too high on a given stage introduces distortion on the signal.
A fair amount of mid-20th century amps (especially for guitar) had just one adjustable gain stage, simply labeled "gain." Musicians and producers found that by cranking the gain very high, the resulting signal distortion actually sounded kinda cool and so they used it as their sound. The term gain gradually became synonymous with distortion, and "volume" or "master volume" was used on output stages to differentiate the output level from the distortion level.
This also holds true in non-guitar amplifiers, like those found in mixing/recording consoles and emulated in DAWs. In these cases the input gain is more for setting the input signal level high enough to get a good noise floor without introducing distortion, so that the signal can be routed to various EQs, effects, and the like. However, a lot of classic microphone preamps like the old Neves and APIs weren't capable of providing noise-less amplification, so the gain on them (and any emulations) is also a distortion level. It's a completely different-sounding distortion, but a distortion nonetheless. The output level is used to set the desired loudness of the processed signal. in the case of a console or multi-track project, the loudness is relative to the master volume of the system, and is used to set the relative signal volume compared to the other tracks.
In my recording experience, I've found a good rule of thumb to get a good-sounding track is to roll up the input level to the point where you just start to get distortion on the highest peaks of your incoming signal, and then back off a touch. The output volume is then set to get your track as loud as you need it, relative to the other tracks in the project. However, the ultimate judge of "good tone" is your ears, so do take the time to find a way that works and sounds best for you.
Comment: *then back off a touch* +1. Then back it off another notch; sound check is at best 3/4s of performance intensity. If you can't monitor it live just watch the DAW to see if it spikes above the cutoff line. Individually(!), proper mic selection and placement should take care of any distortion, with the fader set to zero. Then you can find the problem child in the mix (distorts somewhere above +0) that you have to bring everything else down to... just plug the bass into the direct-out when they're not looking.
Answer: Electrical engineer here.
Gain is the ratio of the output signal magnitude to the input signal magnitude of an amplifier. In idealized circuits, as you turn the gain up, you increase this ratio and the signal's gain increases and it gets louder. Or you reduce the ratio and it gets softer. No distortion occurs.
However, in the real world, even well-designed amplifiers can only reproduce the waveform up to a certain magnitude before the tops and bottoms of the waveform get chopped off. This is called clipping and depends on the maximum upper and lower voltages available to the amplifier.
The "Volume" knob, in terms of circuit design, often routes some ratio of what would be the full output signal (0 to 100%, based on knob setting) to the output of the circuit (jack, speaker, etc.). In this case, max volume represents no (or negligible) attenuation of signal, while 0 volume represents the would-be output scaled down to near-zero amplitude. This knob can only reduce the overall gain of the circuit.
Basically, if you have a well designed piece of equipment and you crank the "Gain" knob, you're more likely to get clipping distortion (sometimes this is intentional, as in tube guitar amplifiers and distortion effects pedals), which you may or may not want. But if you turn down the volume, you're typically just scaling an already gained-up/possibly distorted signal. Sometimes high-headroom amplifier circuits that can be gained up massively without clipping will be called "Volume" on the user interface, but ultimately this will clip if you gained it up without bound too. (This last bit is the difference between high-end $4 apiece opamps and consumer-grade $0.25 apiece opamps, as well as relatively high-voltage supplies for the amplification circuitry.)
So the answer is, as with all things engineering, be it audio or electrical, "it depends".
You really have to follow your ears.
-- EDIT
As you increase gain, you also amplify circuit noise. The general level of this noise is your noise floor, which in layman's terms basically means that any signal of magnitude lower than this noise is indistinguishable from the noise itself and contributes nothing of value to the recording. I typically adjust my gain up to the point where the noise becomes (subjectively) unacceptable, and then back off a bit.
Comment: (decades out of practice) electrical engineer _here_ : thanks for that one phrase "The Volume know can only _reduce_ the overall gain of the circuit". I believe that is the core of the answer to the OP. the rest of the answer is of course great supporting material
Answer: It's as I said in the comment:
Gain is referring to the input, volume to the output.
Volume is how loud the OUTPUT of the channel or amp is. It controls loudness, not tone.
Gain is how loud the INPUT of the channel or amp is. It controls tone, not loudness.
https://www.musicianonamission.com/gain-vs-volume/#targetText=Conclusion%3A%20Gain%20Vs%20Volume&targetText=Volume%20is%20how%20loud%20the,It%20controls%20tone%2C%20not%20loudness.
Edit:

My question is which one is recommended in music production to make music louder without distortion or other bad side effects? Gain amplification or volume increase?

If the gain-level is in the red area it means the input signal is to strong. Thus the best sound will be resulting from a good balance of input and output. That's what will be called a good mix.
Comment: Well, sort of, in the restricted case of a guitar amp where the input stage is designed to make an interesting sound when deliberately overloaded.   But isn't this question about a microphone channel?
Comment: They're all gains, strictly -, but on input, especially with valve, tape [or imitation] it describes the amount of 'distortion' however subtle that is likely to be added as the gain is increased. 'Volume' on the other hand at the output stage is then not meant to add any distortion at all. The two meanings have gained [pardon the pun] distinctions that weren't originally there.
Comment: @LaurencePayne I am not going to limit the question to just microphones. Will definitions vary for gain and volume uses in other systems like DAWs and VSTs?
Comment: @Laurence: I don't see a difference between a microphone channel gain and a guitar amp. I really assumed they buttons are referring to the line in and line out. But  I 'm not sure whether OP's the comment is meant ironical :) As I thought if my assumption was correct it mus be clear for all English speaking people. Now I am surprised that the answer is really welcome. (What often seems to be forgotten  in this SE is that not all users  here are English mother language and that sometimes the things that seem most clear are not clear for other: e.g. the meaning of major/minor or gain/gagner (fr)
Answer: I see answers all over the map on this with some DuckDuckGo-ing, so here is my as-yet-undisturbed understanding:
Gain is a measure of amplification, whereas volume is a measure of limit.  Gain is a control on a circuit which actually amplifies a signal (and its noise, ATBE) whereas volume is a control on a circuit which limits a signal.
Implication: increasing volume too much can distort a signal because the downstream components cannot handle it, whereas increasing gain can distort a signal because either downstream components or the amplifier itself cannot handle it.
I could well be wrong -- I do not have any of my 1980s circuit construction textbooks anymore :-(
Comment: Well, sort of.  A gain control MAY directly affect the gain of an amplifier.  Quite likely the amplifier privides a fixed gain, the gain control merely attenuates the input signal.
Comment: @Laurence Payne - Attenuating an unbuffered input signal increases the impedance on that input and makes it more susceptible to electromagnetic noise, and buffering unnecessarily adds circuit noise and phase shift to the signal. Many non-tube analog circuits adjust the gain feedback directly, and the volume knob attenuates the signal at the end of the gain stage.
Answer: The term "gain" tends not to means nothing specific in the labeling of knobs on commercial audio equipment for music. I've seen plenty of "gain" knobs that actually performed simple attentuation of a previous fixed-gain amplification stage: i.e. simple volume controls.
"Gain" doesn't exclusively refer to amplification in electronics, either. In radio, antennae are said to have different amounts of "gain". An antenna is a completely passive device; it only captures energy.
However, in amplification circuitry, "gain" does refer specifically to an amplifier's amplification factor. A honestly labeled device uses "gain" only for amplification factor controls, and "volume" (or similar, like "output level" or such) for passive attenuation of a signal voltage with a variable resistor.
Gain control influences an amplifier's action by altering the amount of impedance in its feedback circuit. It can affect the signal quality in complicated ways compared to a passive volume control. The frequency response, distortion and noise characteristics of the amplifier are affected by variations in the gain.
Answer: With respect to an audio mixer, gain refers to the pre-amplification of the instrument or microphone signal and volume refers to the volume fader or knob, which is normally a resistor.
Usually volume faders or knobs have a detent, marking unity. They are designed to give the best signal to noise ratio at unity gain, where the signal input equals the signal output. Because different instruments and microphones will have different signal levels at the input stage, you often need to adjust the amount of gain to achieve unity gain to maximize the input's signal to noise ratio. If you have the gain too low, you will need to adjust the volume fader up above unity, raising the noise floor. If you have the gain too high, you may need to adjust the volume fader below unity, again raising the noise floor, but at the gain stage.
Ideally, you want the signal to stand out from the noise floor to achieve the highest signal to noise ratio. If the gain is way too high, it can also clip the signal or distort the signal before hitting the volume fader, so no amount of adjusting at the fader will clean up the signal. It can be a bit overwhelming, but with audio, your ears are your best guide. Different microphones or instruments will perform better with different gain settings, but the best way to find that is to set the fader at unity and start with the gain all the way down, then increase it until the signal sounds clear. Good luck!


How can a very old star be formed among Population III stars?

Question: After looking at some articles about old stars, (this, that, and this Wikipedia article), I thought about how such an old and small star could have formed. As the early universe had very massive, early-type stars and (no? almost none?) smaller, late-type stars. So how could a ~$1M_\odot$ star have formed in the early universe, where massive Population III stars dominated?
Here are my theories, if you may find them helpful.
Mass loss via a long-dead companion
Star Foo and Star Bar are both $300 M_\odot$ stars closely orbiting each other. Star Bar is slightly more massive than Star Foo, causing Star Foo to lose mass to Star Bar. Now, Star Bar is $580 M_\odot$ and Star Foo is now drained to $20 M_\odot$. As Star Bar ages and becomes a supergiant, Star Foo gets engulfed by Star Bar, reducing Foo's mass to $\text{1-2} M_\odot$. Star Bar then goes supernova, ejecting Star Foo. 13 billion years later, Star Foo ages and becomes a subgiant, what we see today.
Formed in a massive star's disk
When the universe was young, there were plenty of materials to create stars. One massive star, star Foo, formed. It had a vast disk of gaseous material, weighing over $2 M_\odot$. In the disk, perturbations caused a massive clump of gas to form together, causing the ignition of hydrogen and creating a small, yellow dwarf of mass $0.8 M_\odot$, called star Bar. When Foo went supernova, Bar was ejected. 13 billion years later, we see an ultra-metal poor, very old, late-G type borderline-subgiant.
Split off from a massive star's envelope
A massive star forming region creates a star, Foo. Foo is very massive and large, and begins losing mass through the stellar wind. In a massive eruption, over $1 M_\odot$ is ejected from the star's envelope. This gas clump collapses under its own weight to form a small, Sun-like star. As the universe ages, we see a metal-poor, very old red giant.
Comment: Where do you get your information that no small stars were formed in the early universe?
Comment: Maybe you suggest a tag-definition for [tag:stellar-population], please?
Answer: Many astronomers and cosmologists conjecture that Population III stars were very massive, perhaps even extremely massive. While this opinion is not universal, it does appear to be dominant. If this is the case, at least some of the very first stars died shortly after they formed, within a million years or less. This in turn would have meant the seeds for the first Population II stars would have been present in some places shortly after the very first stars formed and then died.
The Population III stars did not all form (and die) at the very same time, and those seeds needed to create the first Population II stars would not have been dispersed uniformly. So at least for some period of time in the early history of star formation, there would have been a mix of Population III stars in some places, Population II stars in others.


What is the relationship between the demand for loanable funds and investment?

Question: If the demand for loanable funds decreases, investment increases because the real interest rate decreases. Isn't that a contradiction, because loanable funds are used for investment, and a decrease in demand for loanable funds must come from a decrease in investment?
Answer: Assuming loanable funds are all used for investment, loanable funds = investment.
The interest rate can be though of as the price for loanable funds. Take a look at the following graph.

You can think of the change from point A to C in two steps, with B as the intermediary, even though in reality both steps probably happen simultaneously.
First the shift in demand from D to D2 (decrease in demand for loanable funds) is reflected by the move from A to B. Price has not yet changed at this point.
Then, a new equilibrium is reached with quantity demanded moving down the new demand curve (as price decreases) to point C. In this step price decreases so the quantity demanded actually increases. But it does not reach the quantity demanded at the original point A.
So as the demand curve shifts to the left both price and quantity demanded decrease.
Comment: So, overall, does investment increase even though the demand for loanable funds has decreased? If so, what caused the decrease in demand?


Are the first three values that describe a 3D plane actually a 3D vector?

Question: A 3d plane is typically defined as a,b,c,d. Are a,b,c actually the x,y,z coordinates of a 3d vector, with d defining the rotation of the plane, something like axis-angle rotation data?
Answer: The four-variable representation of a plane is the coefficients in the equality
$$ax + by + cz = d$$
This can be seen as \$N = (a, b, c)\$ being a normal vector and \$d\$ being a distance from the coordinate origin (in units of the-length-of-\$N\$), and we can also write this equation as
$$N \cdot P = d,$$
where \$P = (x, y, z)\$ is the point which the equality tells us is or isn't on the plane.
This representation does not allow defining a specific "origin of the plane" — mathematical planes don't have origins. (However, it happens that since \$N \cdot P = d\$, if we set \$P = (d\left|N\right|^{-2})N\$, then we get a specific point on the plane: the point which is nearest the origin of the coordinate system.)
If you change the = to < or >, you describe a "half-space", which can be used for things such as an infinite floor in a physics engine; the opposite half-space is obtained by negating both \$N\$ and \$d\$.
Comment: Good answer. Just one correction: *d* is more like a *squared distance* (unless (a,b,c) has length 1, which is often the case but not guaranteed).
Comment: @SamHocevar Squared? This is all linear. I think you're thinking of what I phrased as that *d* is in units of *N*.
Comment: oh, it's all right then, sorry!
Answer: "Typically" is a quite subjective word, in my experience there are different way to describe a plane in a 3D space that are more common because of the properties that such constructions show.
About your question, there is away to use 4 real values to determine a plane in a 3D space. As you pointed out, a,b,c may be the components of a vector that is perpendicular to the desired plane. If N =(a,b,c) is our perpendicular vector, you may find a point in your plane that is P = d N for some d real and positive. Here you say that d is the distance from the origin in term of N; if N is a unit vector, then d is the distance between the origin and your plane in the way that the term "distance" is commonly meant.
Surprisingly you can define any possible oriented plane bacause you can use a negative values of d; doing so you loose the direct meaning of d as distance until you put it in an absolute value (|d|).
Answer: As far as I know a plane is usually defined by a position, for telling us where the origin is, and a normal pointing upwards from the plane to tell us what orientation we have. It's common practice to use two vectors for this.
With four variables you don't have enough variables to define a plane that doesn't have an origin at (0,0,0) or not enough variables to account for all rotations.
The minimum we would need for a plane in 3D euclidean space with an origin that's not at (0,0,0) and can be oriented in anyway we want is 5. Imagine the unit sphere, we need 3 variables to define where  the origin of the unit sphere is (X,Y,Z). Then we need two variables to define where the 'up'  of the plane is. We can do this by using the vector described by going from the origin of the sphere towards it's surface given a latitude and longitude.
How you would reconstruct a plane with only four variables I don't know. Maybe you're working in a narrow domain (the plane is always at (0,0,0) and the four variables are a quaternion?) or the variables aren't scalars? In what context are you using this a,b,c,d?
Comment: A plane is usually defined as normal/distance or the four scalars (which is basically the same thing). There is no point because the fourth scalar (the distance from origin) equals dot(point,normal), which is also the most common way to interact with planes (checking which side a point is on / how far is it from the plane) and thus must be the most optimal (no one wants to recalculate the distance in each test).
Comment: I had no idea! I still don't see how you would get all orientations in that case. Could you expand your comment to an answer, that would benefit us all :). *Oops, didn't see FXIII's answer*


What does M mean in the 'Free or Slave' field in the 1850 US Federal Census Mortality Schedule?

Question: What does 'M' mean in the 'Free or Slave' field in the 1850 US Federal Census Mortality Schedule?
Answer: It's probably an error.
The options for the 'Free or Slave' column were just 'Free' or Slave'.  Often, the default was taken to be 'Free', so the values was only entered for slaves with an 'S' in that column.

However, the column to the left of the 'Free or Slave' column is 'Color' with options White (W), Black (B), or Mulato (M).
On the other side, the column to the right of the 'Free or Slave' column  is 'Married or Widowed', with options 'M' for married and 'W' for widowed.
Sometimes people entered the answer in the wrong column, which in this case could end up with an 'M' for 'Mulato', or an 'M' for 'Married' in the 'Free or Slave' column.

In the snippet from an 1850 census page below, the person completing the form entered the 'M' for 'married' in the wrong column on the fourth row.

In this case, someone spotted the mistake, crossed it out, and entered the 'M' in the correct column, but that didn't always happen.
Census takers were human too.
Answer: I believe that sempaiscuba is probably correct with their answer. However, there is a slim possibility that the "M" stands for "manumitted", which is the technical term for the act of a master freeing a slave ("the slave was manumitted" = "the slave was freed by his master"). It seems unlikely that the census taker would use an additional letter instead of just "F" or "S", but I suppose it is possible that they might have been trying to make a distinction between those who were born free and those who were born slaves and then later freed.
A simple transcription error is definitely the more likely scenario, however.
Out of curiosity, is the person in question listed as white, black, or mulatto? Because if they are listed as white, it is definitely a transcription error.


Layer 2 Switch Mac Address

Question: I know a layer 2 switch floods the frame out asking who has a certain mac address. My question is how does it know what mac address to ask for in the first place?
Scenario: A brand new switch is implemented. 5 Hosts a re connected. Host A sends a message to Host B. How does A know what the mac address is of Host B in the first place?
Comment: Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
Answer: ARP (Address Resolution Protocol) is used by a source host to resolve the layer-3 address of a destination host to that host's layer-2 address. An ARP request is broadcast on layer-2, asking, "Who has this layer-3 address?" The host with that layer-3 address will unicast back to the requesting host with its layer-2 address.
Hosts populate an ARP cache with layer-3 addresses which have been resolved to layer-2 addresses so that ARP is only used the first time a host wants to send something to another host. Entries in a host's ARP cache have a timeout, and they will be eventually be flushed if there is no activity for that entry.
A switch only floods an unknown unicast, and switches don't ask who has a certain MAC address. A switch will maintain a MAC address table, which relates a particular MAC address to a switch interface. A switch builds or updates this table every time a frame enters a switch interface. The switch will look at the layer-2 source address on a frame entering an interface, and it will add to, or update, its MAC address table with that address and interface.
A switch will also look in its MAC address table for the layer-2 destination address in the frame to find to which interface the frame should be switched. Only if the switch doesn't find the destination address in its MAC address table does it flood the frame to all other interfaces. Entries in a switch MAC address table have a timeout, and they will eventually be flushed if there is no activity for the MAC address.
Comment: Ron is 100% correct, ARP connects the "dots" for the MAC address table of the switch. When not known what device sits on a an interface and the switch needs to locate this data FF-FF-FF-FF-FF-FF is sent out of all interfaces on the switch. Hosts then  send an arp reply message if is the owner of the mac address, hosts with no match do not reply. The arp reply arrives at the switch,the switch then documents which interface it was received upon in the MAC table. By this method once a MAC address is known a multicast ARP is not necessary for the device in question. SW1>>GE-0/1/1=01:54:1F:A5:FF:05
Comment: Well written answer, but perhaps  `A switch only floods an unknown unicast` should perhaps also mention multicast and broadcast? @TySmith you seem to imply (not sure if it was intentional) that the switch sends FF-FF-FF-FF-FF-FF but this is wrong, as Ron wrote it is the host that sends and ARP request (with destination mac address FF-FF-FF-FF-FF which is the broadcast address and so this is indeed flooded out all ports). And so at the end where you mention "multicast arp", I suppose you meant broadcast??
Comment: It seems we have a different opinion on the definition of *flooding* then, but I guess this becomes more of a semantic discussion. IMHO (and a quick google search seems to reveal that some people agree with you and others agree with me) *flooding* is a generic term for sending  a frame or packet (can be L2 or L3) out on all ports except the ingress port, and  can be used (at L2) for unknown unicast, multicast (without igmp snooping) and broadcast. *Broadcasting* (at L2) is the act of sending a frame to FFFF:FFFF:FFFF. In other words a *host* broadcasts (e.g.) an ARP request on the LAN...
Comment: ... and as part of this broadcast process *the switch floods* that frame. FWIW Cisco seems to refer to "unknown multicast flooding" but not to "broadcast flooding" as far as I could tell from a quick search, so they seem to be somewhat in the middle :) BTW I don't mean to be pedantic about this, as I said I think this is a matter of opinion about semantics, I just think it may be worth considering a minor edit to your answer because some readers might get confused by `A switch only floods an unknown unicast` because the world seems to use different definitions of *flooding*.
Comment: The term "flood" is used for unicast frames to distinguish it from broadcast/multicast frames. A host only floods unknown unicast frames. It will broadcast broadcast frames. and depending on IGMP snooping, it may only send multicasts to interfaces which have requested to be members of the multicast group, or it may broadcast those, too.

Layer 2 Switch Mac Address


How can I tell when a cutting has developed roots?

Question: Is there any way to tell if a cutting has put down roots?  I've had cuttings with healthy-looking green leaves that just never create roots (despite using root powder).  I'd like to discard cuttings that don't root, but I also don't want to break off young roots by tugging on the stems.  Is there any trick for this that won't injure the plant?
Comment: A cutting of what: hardwood, softwood, tropical?
Comment: I'm interested in general answers if possible, though in my specific case I'm dealing with hardwood cuttings
Comment: Any update about the cuttings?
Answer: I assume you're talking about rooting plants in soil.
I'll describe the system I like to use, and tell you how I generally decide when they have roots. I imagine the way to tell may differ slightly depending on your rooting system, which is why I'm explaining mine.

I pot the cutting in fresh seed-starting mix. I add a granulated 7-7-7 fertilizer and rockdust to the soil before potting, since seed-starting mix has pretty much no nutritional value. Whatever you do, don't add a fertilizer with higher nitrogen than potassium and phosphorus: this will not help the cutting root. I normally use a large cutting (4-16" long) as opposed to a tiny one (about 2"), although this should work for tiny ones, too. I usually put 3-4 inches of stem beneath the soil, but less has worked, too.
I water with water that has about a teaspoon of potassium sulfate per gallon of water. I actually water liberally, although that might sound counterintuitive for a cutting, and you probably don't need to water it so much. I believe the potassium sulfate makes it safer to use more water.
Keep the cutting away from bright light for two days.
Put the cutting in bright light after two days, and keep it there.
When the plant starts growing very noticeably, it probably has roots. (Cuttings usually won't grow much without roots; correct me if I'm wrong, but that has always seemed to be the case in my experience.) Given the bright light, this should not take a really long time (at least for the kinds of plants I've been propagating: tomatoes, peppers, watermelon, tomatillos, cucumbers).

If you don't use potassium sulfate you can certainly expect the cutting to wilt after two or three days. However, it should perk up again within a few more days, and by then it likely has roots. However, if you expose the cutting to bright light before two days have passed, it will likely wither fast and not recover, or else be stunted for a while.
I like to use cuttings from indoor plants to avoid outdoor pathogens and insects (like aphids).
The main obstacle I've found in rooting cuttings is damping off disease. This is why I use fresh seed-starting mix (to avoid the pathogens). I've heard sprinkling cinnamon on top of the soil helps, as an alternative to seed-starting mix, but I haven't tried this yet. I do know, however, that 2700k CFL bulbs help to ward off damping off, as does increased sunlight. So if you make sure some of the light you use on the third day is 2700k (not all of the light, though), it will probably increase your survival rates.
Removing lots of leaves from your cutting prior to potting is not necessary if you keep it out of bright light for two days. Otherwise, it's pretty much essential, so as to simulate a less bright environment.
So, with my method, you just tell if it has roots by whether it's growing or not. Also, the lack of damping off pathogens will greatly influence the odds of inevitable roots. Using my method above, I have never had damping off with my cuttings, and I have had a 100% success rate, so far, which I understand is remarkable. I don't guarantee you'll have a 100% success rate with this method. Without this method I have had maybe one out of twelve cuttings survive (including cuttings rooted in water, which also succumbed to damping off after potting, notwithstanding their elaborate roots), and then the only ones that survived had bright light on the soil to prevent damping off. Bright light on the soil may actually be all you need, but I would need to experiment with infected soil more to be sure, and it's perhaps a task to get bright light on the soil without getting it on the leaves the first two days. Maybe cinnamon would help there instead.
I would further note that potassium sulfate will likely greatly increase your success rates, and rooting speed, too. I recommend it if you're into cuttings. I imagine it speeds root growth. It certainly makes plants stronger.
You do not need hormone rooting powder with this method (at least  for tomatoes, peppers, tomatillos, cucumbers and watermelons). You may or may not need it for other stuff.
As an alternative to this method, if you're taking cuttings of houseplants, like spider plants, golden pothos, aloe vera, ivy, creeping Charlie, wandering Jew, Christmas cactus, Easter cactus, and such, in my experience, rooting them in water and potting directly into potting soil afterward works reasonably well (at least it did when I was a teenager when I tried it last). When rooting in water you can see the roots to know they have roots, of course. Potting soil doesn't work so well with vegetables by comparison, probably due to the higher nitrogen content. I don't know if the potting soil I used as a teenager was pre-fertilized.
It should be noted that seed-starting mix and potting soil are not the same thing, even though they look pretty much the same.
Comment: Have you had luck applying this to trees or other woody, slower-growing plants?  To be fair - waiting for growth is a reasonable idea even for trees, since you can time your cuttings to coincide with the growing season.
Comment: An excellent answer!  I plan to leave it open for a few days to see if we get others as well.  You're correct - I am referring to plants in soil.
Comment: @JohnWalthour Thanks, and that's cool. I haven't tried this with trees or particularly woody plants, yet. I can't say if it would work, but I plan to experiment, perhaps.
Comment: You might consider rooting woody plants in a narrow, clear container (like glass) so you can see the roots from the glass soon after they grow. This may or may not affect the process, and it will probably be difficult to remove the plant. Clear plastic that you could cut apart might be better. A clear container may or may not help against damping off, too. However, you might have a problem with algae if you keep the plant in the clear container very long.
Answer: Excellent reply and thank you. All I have to add is that when those babies are coming along happily into another seasonal expected change, such as mid autumn or winter, I let them be in their original container and pot up when the weather is forecast as to be more consistently warm.
I'm in a temperate Australian climate and here, now, we are in a warm autumn and headed for a warm winter. I know that in the next weeks the day time temps will still be hot (29-32 deg. C) but night time will be considerably cooler or cooling. Yes, sure I can put my little ones (a month old) in to the ground but night temps may cause issues as may any unusual here, frost. Watch the long term meteorological forecasts by government agencies, not just the news!
Answer: Best way to tell if it has put down roots is to note whether it has died. Sound obvious but sometimes a green cutting can last for a long time without roots, but eventually it will dry out and turn brown. If you see any new buds or growth, that's an indication that something is going on down below. I root in clear plastic so I can see root development. If I see a white root, I know I'm good. Another way to tell is to gently tug at it after a month or so. If it slides right out, you are out of luck. If it resists, you're good.
I usually get roots after six weeks when rooting woody plants like trees and roses, but never 100 percent, so root more than you need.
But to increase your odds - if you're rooting woody plants you don't need any fertilizer or sulfates or anything similar. And you want to remove most of the leaves on the cuttings. And you don't want the cuttings in direct sunlight.
Why?
Because in the first place you're trying to get the plant to grow roots. Fertilizer will not help that process. Fertilizer is only useful once you have an established plant with roots and leaves.
In the second place, roots take up moisture and nutrients. Without roots, there is no water uptake. Leaves evaporate water. if you have lots of leaves evaporating water and no incoming water through the roots, your cutting will die.
Finally, direct sun will only help once you have new growth. Prior to that, the leaves you've left will be fine with indirect sunlight.
You will know the plant has rooted if after a month or two it is still alive, the leaves haven't fallen off, and new growth is apparent. After a few weeks, you can gently tug at the cutting and if it sticks, you're OK. But I think it's better to just be patient. Then, when you re-pot, don't plant too deeply in the new pot. Keep the roots near the surface so they don't suffocate.
And there's some research suggesting that putting your cutting into a larger pot helps the roots "sense" how much room they have and you get larger plants by putting the small, newly rooted cuttings into much bigger pots than you were planning to. In other words, a 16 oz pot vs a gallon pot.