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Multi-Channel Discrete Audio to 2-channel surround format (i.e. DPL-II
mp3weenie
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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DVDdoug
post Apr 6 2010, 20:43
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In general, this doesn't work very well. You're usually better-off just using the stereo mix (or the mixdown) and one of the Pro Logic "soundfields". Pro Logic (movie mode) works by steering which works OK for movies, but doesn't work that well for music. The discrete 5.1 mix was not done with steering in mind, and screwy things can happen. It's possibe to manually create your own mix/mixdown while monitoring with a Pro Logic decoder, but I'd say it's not worth the trouble.

QUOTE
I am not sure I need a DPL-II encoder, but something compatible with matrix processors.
The only true (software) Pro Logic encoder I know of is SurCode ($800 USD!!!).

But just for kicks, I once created a "fake" Pro Logic encoding (with a regular audio editor). The steering worked surprisingly well!
Front Left - Panned fully left.
Front Center - Left & right identical and in-phase.
Front Right - Panned fully right.
Rear Left - Left & right 180 degrees out-of-phase, delayed ~20ms, panned 75% left.
Rear "Center" - Left & right identical but 180 degrees out-of-phase, delayed ~20ms.
Rear Right - Left & right 180 degrees out-of-phase, delayed ~20ms, panned 75% right

NOTE - The settings I used were not exactly correct (see Wikipedia).

QUOTE
DVD-Audio discs: with DTS tracks
DVD discs: with DTS tracks
DTS-CD discs: CD with DTS encoded tracks
DTS Audio encoded WAV files.
Commercial DVDs are copy protected. I won't discuss how to "crack" copy protection, but there are websites that specialize in that kind of thing.

I've never decoded/transcoded a DTS file, but it's probably going to take a handful of tools for your various formats. Here are some tools that might be helpful:
AC3filter (FREE!!!).
Audacity with the optional FFmpeg library (FREE!!!).
XRECODE II ($15 USD).
VOB2MPG (FREE!!!).
AoA Audio Extractor (FREE!!!).

This post has been edited by DVDdoug: Apr 6 2010, 20:47
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mp3weenie
post Apr 7 2010, 00:14
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DVDdoug,

Thanks for the input. I was thinking the best would just to monitor/record a DPL downmix. I would definitely want to use the music mode. I agree it may not be worth my time but I would like to see how the downmix through a matrix decoder performs with discrete multi-channel music. What application would you recommend that has a DPL-II "music" downmix mode from which I can monitor/record?



Thanks! Jay
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DVDdoug
post Apr 7 2010, 02:40
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QUOTE
What application would you recommend that has a DPL-II "music" downmix mode from which I can monitor/record?
Once you've decoded your DTS files to either 5.1 channel WAVs or 6 separate WAVs, you can downmix with any audio editor. Audacity should work. When I made my "fake" dolby surround file, I used GoldWave. (GoldWave is only 2-channel stereo so I made 6 seperate WAV files and mixed them into a new stereo file.)

For decoding/monitoring, if you're lucky, your soundcard has a Pro Logic decoder. If not, you can run your soundcard output into a Home Theater recceiver.

I don't believe there is any steering in the "music" mode. So, mixing should be easier.
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mp3weenie
post Apr 9 2010, 17:42
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QUOTE (DVDdoug @ Apr 6 2010, 21:40) *
QUOTE
What application would you recommend that has a DPL-II "music" downmix mode from which I can monitor/record?
Once you've decoded your DTS files to either 5.1 channel WAVs or 6 separate WAVs, you can downmix with any audio editor. Audacity should work. When I made my "fake" dolby surround file, I used GoldWave. (GoldWave is only 2-channel stereo so I made 6 seperate WAV files and mixed them into a new stereo file.)

For decoding/monitoring, if you're lucky, your soundcard has a Pro Logic decoder. If not, you can run your soundcard output into a Home Theater recceiver.

I don't believe there is any steering in the "music" mode. So, mixing should be easier.


I am new to doing the "fake" phasing you suggested above. I am now thinking that this is what I want to do. Ideally if there was a codec chain that would take DTS and expand to 5.1 ( I think I found a codec that does this), then apply the correct phase for each channel, then mix down to stereo in real time.

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.

THANKS!
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DVDdoug
post Apr 9 2010, 19:57
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QUOTE
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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