question about left channel frequency information in stereo mode

Hi there:
 
I met with a new problem in the stereo mode: The two channels have different sound information and I only need to detect a tone with the specific frequency in the left channel. What changes shall I make for the following formula if I have two channels and each channel has 576 units pcm information. 
 
Thank you!

shiming

> 1. I use mad library to get the pcm data of a marker tone, each frame 
> contain 576 samples. I turned each 16 bits integer samples into floating 
> point by divided by 32768. And I put it into a floating point array 
> pcm[576]. 
> 
> 2. I tried to do fourier transformation to those pcm data:
> Fk = sum (pcm[i] * cos(2*pi*k*i / N))
> 
> N = 576
> i: from 0 to N
> k: from 0 to N / 2
> F[288]: is a floating point array
> 

Thank you!
 
shiming


		
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