| Hey Paul,
Sounds like what you're looking for is a way to matrix a stereo file
into m/s (middle/side) format. As I understand it, the formula to
accomplish this is as follows:
L+R = M
L -R = S
The M signal is your middle channel. The S signal you pan left (S+),
then bus to the right channel and throw out of phase (S-). If this is
done correctly, summing the S+ and S- signals should cause total
cancellation.
This should create the three channel effect you're looking for, and it
can be derived from stereo files. I've never done this with csound, but
it should be possible, and I would be very interested in seeing any
working or betaexamples...
Hope this helps.
Cliff
Paul Winkler wrote:
> Howdy. I have an interesting (I hope!) signal processing question that
>
> arose on a pc soundcard newsgroup. Some web searching didn't turn up
> much, so I thought I'd see if anyone here had some ideas.
>
> The goal is to extract the "center" portion of a stereo soundfile;
> that
> is, to be able to end up with three outputs:
>
> --"pure" left information--nothing that is also found in the right
> input
> channel
> --"center" information--only things found in both channels
> --"pure right" information--nothing found in the left input channel.
>
> The first thing I thought of was to simply subtract one channel from
> the
> other, i.e. L-R. The problem is that, while this does eliminate all
> "center" information, it also results in the pure left combined with
> an
> out-of-phase pure right, and no way to separate the two.
>
> Someone else suggested doing this:
>
> L output= 2L - R
> R output= 2R - L
> ...which doesn't help all that much. We now have two different
> signals,
> each of which has attenuated "center" information, but each also
> contains some out-of-phase information from the other. It looks like
> there is just no simple arithmetical way to do the job.
>
> The last suggestion that came up was to do a FFT of each channel,
> compare the information from the two FFTs, and use that to filter each
>
> channel. Implementing this is a bit beyond me and I can't figure out
> whether or not it would be effective.
>
> Any ideas?
>
> Alternatively, has anyone already designed a csound instrument to
> accomplish this task? Or is there any other shareware/freeware tool
> that might do the job?
>
> Thanks much,
>
> Paul
>
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