Measuring Audio Signal Similarities I have recorded samples of lungs sound (person breath) signals from electronic stethoscope.
How can I measure (In percentage) the similarity between two audio signals (lung sound), the general idea is to take a clean recorded signal(without environmental noises, Laboratory conditions) and compare it with the regular recorded lung sound. If the percent is high enough then it is valid, else it is with too much environmental noises.
I thought to do it by cross-correlation but after a research I found out that it is more suitable for time lag between signals. Any good idea to start with? I want to implement it in MATLAB.
** the recorded files are in AAC format.
You can use the Normalized Cross Correlation for that.
http://en.wikipedia.org/wiki/Correlation_and_dependence

Basically, representing each recorded sound as a vector, this gives the angle between them. 

Another approach is dealing with features of the sound instead of the signal itself.
You can start by reading how Shazam works:

https://www.google.com/webhp?sourceid=chrome-instant&amp;ion=1&amp;espv=2&amp;ie=UTF-8#q=how%20shazam%20works

http://www.reddit.com/r/askscience/comments/1mdb08/how_do_apps_like_soundhound_and_shazam_work_is/

http://gizmodo.com/5647458/how-shazam-works-to-identify-nearly-every-song-you-throw-at-it

http://www.slate.com/articles/technology/technology/2009/10/that_tune_named.2.html

http://en.wikipedia.org/wiki/SoundHound

http://www.quora.com/How-does-SoundHound-work

http://everythingelsematterstoo.blogspot.co.il/2010/11/how-shazam-works.html