Nexus 5X: How can I use custom ringtones /alarms without installing additional apps? I have a Nexus 5X with Android 6.0.1 and latest security patches (June 2016). I try to use my own soundfiles for alarms and ringtones. I tried a lot of suggestions, but I can't get it to work. When I want to select my sounds, only the default sounds appear in the list.

First I tried to add them to the folders (/Alarms and /Ringtones) with the built-in file explorer. I could copy the files, but only the alarms were selectable, not the files in /Ringtones. So at that time alarms were fine, ringtones were not.

Here someone suggested that it could make a difference if the files are copied from a PC via USB cable. So I tried that, but it did not make a difference.

Someone suggested that the files might only be selectable after a reboot. So I rebooted and now it is worse than before: I cannot select my own alarms and ringtones. For both settings, only the default sounds appear.

I don't want to try the recommended "ES File Explorer" or the "Zedge ringtone &amp; wallpaper" app. This problem must be solvable without any additional software. Does anyone have an idea how to find out why this is not working?

By the way: I tried sound files in different formats (mp3, flac, ogg). All files can be played on the phone. They worked perfectly as ringtones and alarms on my previous phone. The filenames do not contain any special characters.
I finally found a solution: I deleted all files in /Alarms and /Ringtones and rebooted. Then I copied just one mp3-file to each folder with the built-in file explorer (I guess it does not matter which app you use or if you do it via pc/usb). This mp3-file could be selected in alarm and ringtone settings.

My first idea was that one of the files that were in /Alarms and /Ringtones before was damaged or in a not supported format. So I copied back the other files. To my surprise it is still working and I can also select the other files. So I don't really know what caused the problem, but this work-around solved it.

So if you have a similar problem, it may help to delete all files in that folders (make a backup somewhere else), reboot and then copy the files back.