So I know how to plot fft the audio file within Matlab and a window pops up. My question is, what next? I want to know how to go about measuring the frequency(s). I have two similar audio files, of two people saying the same thing, and i want to see if there's a relationship (correlation) between their voices in terms of frequencies and speed (bpm)
Speech processing is a very long and detailed topic, but let's make a start.
This probably won't work, but the first thing you can try is cross-correlation of the signals.
xc = xcorr(speaker_1, speaker_2);
Note that really all you may get out of this is the delay between each sample (if you're lucky).
You might also get some level of correlation coefficient by taking the peak value of
xc = xcorr(speaker_1/std(speaker_1), speaker_2/std(speaker2));
If that doesn't work (I'm not hopeful), you will need to look at lots of other options: