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Multi-Channel Discrete Audio to 2-channel surround format (i.e. DPL-II
post Apr 6 2010, 14:47
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Hi I am new to the forum so I appreciate your help in advance.

I have a dolby pro logic IIx decoder in my car and I am interested in taking my multi-channel audio releases and mix them down to a 2 channel surround mix (phased downmix) so I can put on my ipod and play in my car retaining the surround mix of the original recording. I currently have a DPL-IIx decoder but may also have a Logic7 processor in the future.

So I have audio recordings in the following formats but I am mainly interested in DTS->DPLIIx or similar matrix down-mix.

DVD-Audio discs: with DTS tracks
DVD discs: with DTS tracks
DTS-CD discs: CD with DTS encoded tracks
DTS Audio encoded WAV files.

I am not sure I need a DPL-II encoder, but something compatible with matrix processors. Ideally this conversion could be done in better than realtime if possible.

Any guidance would be appreciated.

Thanks. Jay
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post Apr 9 2010, 19:57
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From: Silicon Valley
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In any case please let me know how you applied the phase to your wave files? I have no clue how you applied the phase.
What audio editor are you using? Usually this is called "invert". The idea is to invert one channel, not both. Then, they are "out-of-phase".

As a quick experiment with your audio editor -
1. Create a mono file.
2. Copy the mono signal into the left & right channels of a stereo file (both channels identical).
3. Invert one channel (both channels identical, but out-of-phase).

When you play the file in stereo, it should sound "strange" and "spacey".
When you play the file in Pro Logic Movie Mode, it should come out of the rear speakers.

Note that the actual Dolby spec does not call for a simple 180 degree phase difference. The left is supposed to be +90 degrees, and the right -90 degrees. But, a 90 degree phase shift (at all frequencies) is not something you can do with a standard audio editor. And, because we can't get + and - 90 degree phase shifts, it's helpful to add some delay to "randomize" the phase differences between the front & rear channels. (There is a relationship between phase, frequency, and delay.)

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