removing vocal from audio file
If my guess is right, your code show you trying remove the vocal from  second audio, the first audio must be the original vocal and the second is some mix (vocal + music)...

So if my guess is true start trying a simple approach to test, here my simple test.

I get just 4096 points of some audio voice and mix with a sine 4096 points in 200hz sampled in 1600hz, all mono.

Plot 4096 voice points:



Now plot a sine in 200 Hz:



Now the Mix (sine + voice):



Now to get the original sine without the voice you need do:

real((ifft(fft(mix) - fft(voice_Signal))))


The final plot after the step above:



course is a very simple test, and in this case we're telling you to have the original clean audio voice before being mixed ...