# Audio codec analysis in MATLAB: crosstalk

I am currently making an analysis of a codec system that can encode up to 2 wave files into 1 file and decode it. Here is a simple illustration:

L+R ---> ENC --->L'+R'
with L'=L+∂1 & R'=R+∂2


The codec is not lossless and we are analyzing if there is any leakage from one source to another, some kind of crosstalk, if you will.

So what I have to do is find out if ∂1 has traces of R & ∂2 has traces of L.

I feel a general approach would be to subtract L/Ldec to get ∂ and then compare that ∂ to R.

I have done some reading on correlation but it's all a little vague at the moment.

So, onto my question(s):

• Is this possible with limited knowledge of DSP (reading up but it's a lot & not that easy)?
• If not, on what should I do some reading (From what I've gathered so far: correlation & Pearson's coefficient)?
• Is there some sort of standardized test for this - I presume there is but I can't find any!

Even though code snippets would be handy since I only just started to use MATLAB & still am somewhat inexperienced, the main point of this topic is understanding so I can implement it. If someone else implements it I won't learn!

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Is decoded L1' different from L1 in this compression scheme, even in no leakage case, or is it only the leakage that changes it? – Andrey Rubshtein Nov 8 '12 at 13:52
Do you expect the original two channels $L$ and $R$ to be uncorrelated with one another, or are they something like stereo channels of a common recording? If they are correlated before the encoder, then checking for cross-correlation after the decoder probably isn't going to be a good approach. – Jason R Nov 8 '12 at 15:34
It's an audio codec, so most of the time L/R are going to be correlated at least partly. For my fiddling-around-test-setup I used a 3khz sine signal & a 5khz sine signal and encoded/decoded them. it turned out that the correlation coefficient for (∂L,R) and (L,∂R) was respectively 0,0002 & 0,0007. I concluded that the leakage was negligable! – King Broos Nov 12 '12 at 9:32