I want to know how to use a music file chosen by the user, then detect when a certain sound frequency. ANDROID

Question

So basically I want this to get the range of 60 - 150 Hz which is the general area for bass that lies in a song. Whenever it is in this range I want it do a function, and only it the range, my problem is I have tried to look up the functions needed to do so but with no luck, if one could show me here or a good article or explanation on this it will be great! I appreciate all the help and I will continue looking on my own. If more explanation is needed I can provide whatever information that is needed!

Austin.

UPDATE: I simplified an algorithm here:

1. User selects the song they want
2. Song loads onto player
3. Function scans song and finds the lower frequencies throughout the song and the output is a pattern.

Answer 1

Step 1) Do a fast fourier transform: http://en.wikipedia.org/wiki/Fast_Fourier_transform

An FFT takes a piece of sound and transforms it into the frequency/time domain - as in, which frequencies are playing and how intensely and during what parts of the sound. This is a useful mathematical operation that relies upon the property that all sound, no matter how complex, can be fundamentally constructed out of one or more sine waves of different frequencies and amplitudes.

If you've ever looked at a spectrogram, for example in foobar2000, it is implemented using FFT:

I suggest instead of trying to implement FFT yourself you find a library that is well tested and fast, such as http://en.wikipedia.org/wiki/FFTW which is written in C

Step 2) Now that you've FFTed the part of the sound that the user is listening to, you can simply inspect the frequency bins and do whatever you want! Although detecting bass kicks is not as simple as 'is this frequency bin a high value?' because then you may mistake bass lines for bass kicks. You may need to do further testing and research to get it to work juuust right.

EDIT: Delyan suggests http://www.clear.rice.edu/elec301/Projects01/beat_sync/beatalgo.html and it looks pretty good.