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Pro Logic's Center Channel Extraction, Implementation questions
wswartzendruber
post Jul 23 2011, 05:31
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I'm trying to figure out how Pro Logic implements center channel extraction. Looking at how various different types of sine waves combine (a single one into two other ones), I guess I'll need to implement some type of FIR filter. I'm very new to this. It would be nice if this could be done on a sample-by-sample basis.

Any help?
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wswartzendruber
post Jul 27 2011, 20:47
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My goal is to implement a Pro Logic decoder with finer grain control over what to do with cross talk.

Problem: When inputting L and R into Lt and Rt, anything perfectly out of phase between L and R gets erroneously sent to the surround channel upon decoding.

Solution: Decode the "surround channel" (crosstalk) on just L and R, and then apply the crosstalk equally to both sides and in phase.

Summary of Methodology:

1. Phase-shift L by +90 degrees and R by -90 degrees.
2. Find the common signal and extract it.
3. Phase-shift L by -90 degrees and R by +90 degress (to put them as they were originally but without the crosstalk).
4. Apply the extracted signal equally to both L and R.

Caveat: Anything originally having a hollow sound will be decoded into the center channel.

The final product will likely have a slider letting the user choose how much phase shift to apply to the cross talk. 0 degrees (to each channel) leaves it alone and 90 degrees puts it perfectly in phase.

I am operating under the assumption that step #2 should be done similarly to Pro Logic's center channel decoding.

This post has been edited by wswartzendruber: Jul 27 2011, 20:49
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