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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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DVDdoug
post Jul 28 2011, 18:20
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OK... Time to start writing some experimental code!

Once you can read an audio file into an array (or each channel into an array), it's easy to add or subtract the L & R channels and put the result in a new array. I don't actullly know how to make a 90 degree phase shift (Hilbert transform?), but I'm sure you can look it up.

I think you will find that there are serious limitations with matrix encoding... We tried to warn you! biggrin.gif
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dc2bluelight
post Jul 29 2011, 04:32
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QUOTE (DVDdoug @ Jul 28 2011, 12:20) *
OK... Time to start writing some experimental code!

Once you can read an audio file into an array (or each channel into an array), it's easy to add or subtract the L & R channels and put the result in a new array. I don't actullly know how to make a 90 degree phase shift (Hilbert transform?), but I'm sure you can look it up.

I think you will find that there are serious limitations with matrix encoding... We tried to warn you! biggrin.gif

90 degree phase shift between channels can only be had by applying a huge, multi-stage all-pass network to each channel so that phase is constantly rotated throughout the audio band, then where you want 90 degrees, build the next all-pass network so it's 90 degrees off-set from the first one.

Yes, we tried to warn you. Crosstalk is part of the matrix. ProLogic was the fix. PLII was an improvement, but not really in crosstalk. ProLogic music on CD's been done (not a commercial success). Do your 5.0 on DVD Audio or Bluray, you'll be happier.

BTW, ProLogic was designed for film soundtracks, the steering time constants being optimized for sound effects and speech. Have fun with music.

This post has been edited by dc2bluelight: Jul 29 2011, 04:37
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