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PCM to 5.1

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I have heard some people talking about generating a 5.1 mix from the PCM audio track on the laserdisc. As far as I am aware, the PCM is 2 channel, so how is it possible to derive five (.1) isolated channels from it?

Any takers?

El Lono
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I'm the one who did it. I used a program that simulated a Pro-Logoc II decoder, which extracts the center and surround information from a stereo source, much like a receiver would. It then saves each channel as a separate WAV file. These WAV files were fed into a Dolby Digital encoder, essentially storing the Pro-Logic information in AC3 form. It took months to research and perfect, but it sounds pretty good overall. Maybe I'll put up a short segment for people to listen to.

[EDIT] More specifically, the software simulated a Pro-Logic II reciever, which can give more of a "split surround" effect than regular Pro-Logic can. Technically, Pro-Logic II is specifically designed for stereo sources, but I figured what the hell.

<span class=“Italics”>MeBeJedi: Sadly, I believe the prequels are beyond repair.
<span class=“Bold”>JediRandy: They’re certainly beyond any repair you’re capable of making.</span></span>

<span class=“Italics”>MeBeJedi: You aren’t one of us.
<span class=“Bold”>Go-Mer-Tonic: I can’t say I find that very disappointing.</span></span>

<span class=“Italics”>JediRandy: I won’t suck as much as a fan edit.</span>

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@MeBeJedi: During your research, did you read this:
It is best to transmit two-channel matrix-encoded material as such to the consumer, and
not decode it in the studio to derive an "artificial" discrete multichannel mix. For one
thing, the results can vary from the intent of the original producer/director, especially if
extra processing has been added on top of the surround decoding in the studio. Also, the
sound will fail to meet listener expectations for true 5.1-channel material.

In addition, many consumers do not yet have a full 5.1-channel Dolby Digital playback
systems, and connect their DVD players' two-channel outputs to a stereo or Dolby
Surround Pro Logic system. Under these circumstances, the Dolby Digital decoders in the
players "downmix" multichannel soundtracks "on the fly" to mono, stereo, or Dolby
Surround matrix-encoded stereo. If the multichannel soundtrack was derived from a
matrix-encoded two-track master, there may be downmix quality problems due to phase
effects from the original matrix encoding. In nearly every case the original Lt/Rt mix will
give the best results.
I read this and decided to just have the plain 2-channel Dolby Surround mix on the DVDs I am making.

Of course if you are happy with your mix, and it sounds like you have put a lot of work into it, then this might not be relevant. I'd be interested to see people's comments if you post links to some samples.

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At the time, I was doing it to save space. The resulting AC3 file was a Gb smaller than the PCM file.

And again, before judgements are passed, let me upload some sampls.

<span class=“Italics”>MeBeJedi: Sadly, I believe the prequels are beyond repair.
<span class=“Bold”>JediRandy: They’re certainly beyond any repair you’re capable of making.</span></span>

<span class=“Italics”>MeBeJedi: You aren’t one of us.
<span class=“Bold”>Go-Mer-Tonic: I can’t say I find that very disappointing.</span></span>

<span class=“Italics”>JediRandy: I won’t suck as much as a fan edit.</span>

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Here's a 40Mb zip with three scenes. It's saved as a DVD file, so you can load it in to your software DVD player and cycle between the 3 soundtracks (there's also some commentary). The AC3 is noticeably quieter than the PCM, but this is not unusual. If you don't have 5.1 playback, then there's no real point to downloading it.

<span class=“Italics”>MeBeJedi: Sadly, I believe the prequels are beyond repair.
<span class=“Bold”>JediRandy: They’re certainly beyond any repair you’re capable of making.</span></span>

<span class=“Italics”>MeBeJedi: You aren’t one of us.
<span class=“Bold”>Go-Mer-Tonic: I can’t say I find that very disappointing.</span></span>

<span class=“Italics”>JediRandy: I won’t suck as much as a fan edit.</span>

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Hmmm..I guess my only question would be, if the source is 2.0, the original mix for the film was 2 channel, wouldn't it be better to use the disc space the interpolated channels you've created take up to improve the video quality? Or is there not a huge difference between the size of the 2.0 and the faked-out 5.1?
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A 2.0 Surround AC-3 track would be about 57% smaller than a 5.1 AC-3.
The uncompressed 2.0 PCM, as MeBe said, is much larger.

But you have to put it into perspective that the 5.1 mix takes up only about, say 10%, of the total disc space. So in reality there's not much gain.

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Agreed. Furthermore, DD 2.0 tends to sound much worse in DD mode, and generally needs to be decoded in Pro-Logic mode to sound decent. I figured I'd leapfrog over that and create a Pro-logic II soundtrack that could be stored and played back in 5.1 mode, especially since my receiver doesn't have Pro-logic II built in. Creating this soundtrack covered several bases at once for me. Plus, I wanted to see if I could do it.

"But you have to put it into perspective that the 5.1 mix takes up only about, say 10%, of the total disc space. So in reality there's not much gain."

Yes. 1.3 Gbs, versus 380 Mbs. And believe me, the video was maxed out as much as possible. I had less than 1% remaining on the DVD (I had to recompile a few times to get it perfect - which is tough, since it takes 20+ hours to compile each time.)

<span class=“Italics”>MeBeJedi: Sadly, I believe the prequels are beyond repair.
<span class=“Bold”>JediRandy: They’re certainly beyond any repair you’re capable of making.</span></span>

<span class=“Italics”>MeBeJedi: You aren’t one of us.
<span class=“Bold”>Go-Mer-Tonic: I can’t say I find that very disappointing.</span></span>

<span class=“Italics”>JediRandy: I won’t suck as much as a fan edit.</span>

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So, to recap:

The 2 channel PCM, actually contains further channels, that can be read and divided by a Dolby decoder/reciever, so you have split these channels and recombined them to 5.1?
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Exactly. The PCM file is a matrixed stereo file. This is why you don't hear dialogue in the rear speakers in Pro-logic mode (actually, you can hear it a tiny bit, because it's not a discrete-channel recording, but you would have to really strain to hear people talking.)

[EDIT]Make your downloads quick. That file won't be there for long.

<span class=“Italics”>MeBeJedi: Sadly, I believe the prequels are beyond repair.
<span class=“Bold”>JediRandy: They’re certainly beyond any repair you’re capable of making.</span></span>

<span class=“Italics”>MeBeJedi: You aren’t one of us.
<span class=“Bold”>Go-Mer-Tonic: I can’t say I find that very disappointing.</span></span>

<span class=“Italics”>JediRandy: I won’t suck as much as a fan edit.</span>

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Ah, cool. I've not had particularly much experience with audio encoding yet. Thanks for the explanation.
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Originally posted by: El Lono
So, to recap:

The 2 channel PCM, actually contains further channels, that can be read and divided by a Dolby decoder/reciever, so you have split these channels and recombined them to 5.1?

It's called Dolby surrond is teally a MATRIXED stereo track...

Dolby Surround 101 - The Matrix

Clearly, the concept is to store additional audio channels on two conventional stereo channels. The technique is to "matrix" the audio channels, a concept originally conceived and patented by Peter Scheiber and subsequently applied by Dolby Laboratories. Simply stated, if the sound mixer wants to place a sound in the front center speaker, he would add that signal at equal amplitude and equal phase to both the left and right stereo channels. If the sound mixer wants to place a sound in the surround speakers, he would add that signal to the left stereo channel shifted by 90 degrees, and add the same signal to the right channel shifted by -90 degrees (so the surround information is of equal amplitude and 180 degrees apart - inverted - on the stereo channels). When such a matrixed stereo program is passed through a Dolby decoder, the sum of the left and right becomes the center. (The center is needed to position certain sounds at the center of the screen for off-center viewers, dialog in particular.) The difference between the left and right channels becomes the rear. I'll remind you that Dolby Surround channels are indeed monaural. The disadvantage of this passive decoding system is that separation between adjacent channels (L-C, R-C, R-S, or L-S) is only 3 dB.

Dolby Surround 102 - Pro Logic

Dolby Pro Logic enhances Dolby Surround by using a number of techniques to increase the separation between adjacent channels. Cancellation subtracts the left channel from the right and subtracts the right channel from the left. This has the effect of greatly reducing sounds intended to be directed to the center speaker in the left and right channels; signals that are common to both left and right are removed. Pro Logic controls this process by detecting sound dominance and its direction. If a sound is found to be significantly louder in any one direction such that it exceeds a predefined threshold, a fast acting voltage controlled amplifier enhances the dominant signal. These techniques may yield adjacent channel separations in excess of 30 dB for static test signals, but may exhibit problems for dynamic program material. (For the sake of this discussion, I'll omit descriptions of such manipulations as phase and pitch shifts to diffuse the surround sound, rear channel bandwidth limitations, and noise reduction - these processes are not relevant to front channel processing of Dolby Digital surround channel information.)


Ripped from DVDFILE.com

Dig?

BONG!

Snoogins...

“My skill are no longer as Mad as the once were” RiK

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"Dig?
BONG!
Snoogins... "


Showoff!

<span class=“Italics”>MeBeJedi: Sadly, I believe the prequels are beyond repair.
<span class=“Bold”>JediRandy: They’re certainly beyond any repair you’re capable of making.</span></span>

<span class=“Italics”>MeBeJedi: You aren’t one of us.
<span class=“Bold”>Go-Mer-Tonic: I can’t say I find that very disappointing.</span></span>

<span class=“Italics”>JediRandy: I won’t suck as much as a fan edit.</span>

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Originally posted by: MeBeJedi
I'm the one who did it. I used a program that simulated a Pro-Logic II decoder, which extracts the center and surround information from a stereo source, much like a receiver would. It then saves each channel as a separate WAV file.


Which software did you use? I was not aware that such software exists!

Han: Hey Lando! You kept your promise, right? Not a scratch?
Lando: Well, what’s left of her isn’t scratched. All the scratched parts got knocked off along the way.
Han (exasperated): Knocked off?!

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Graphedit: to act as the Pro-Logic II decoder and create a multichannel WAV
Hexedit: to adjust the hexadecimal values in the WAV
BeSweet: to split the WAV into 6 separate WAV files (L,R,C,SL,SR, although LFE effects were merged into the other 5 WAVs)
Vegas: to compile the 5 WAVs into an AC3 file

Certainly not your typical "5.1 LD remix".

<span class=“Italics”>MeBeJedi: Sadly, I believe the prequels are beyond repair.
<span class=“Bold”>JediRandy: They’re certainly beyond any repair you’re capable of making.</span></span>

<span class=“Italics”>MeBeJedi: You aren’t one of us.
<span class=“Bold”>Go-Mer-Tonic: I can’t say I find that very disappointing.</span></span>

<span class=“Italics”>JediRandy: I won’t suck as much as a fan edit.</span>

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Which decoder, specifically did you use to derive the ProLogicII channel dispersion (I'm assuming it's a DirectShow filter, since you said Graphedit)? Whenever I try to play back Dolby Surround matrixed PCM (for example, in the TR47 set, or in your samples) using AC3Filter (v1.01a) set to ProLogic II mode I only get 2-channel output.
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I have the procedure typed up. When I get home, I'll put it up.

Oops, nevermind. I found it. 2.0 to 5.1 Pro-logic.

Here's an upgraded version of the same thing. LINK

<span class=“Italics”>MeBeJedi: Sadly, I believe the prequels are beyond repair.
<span class=“Bold”>JediRandy: They’re certainly beyond any repair you’re capable of making.</span></span>

<span class=“Italics”>MeBeJedi: You aren’t one of us.
<span class=“Bold”>Go-Mer-Tonic: I can’t say I find that very disappointing.</span></span>

<span class=“Italics”>JediRandy: I won’t suck as much as a fan edit.</span>

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Time
seeing as mebe created a 5.1 some time ago from his captured PCM track, I thought I'd ask the obvious.

how did you seperate the captured stereo PCM into the seperate dolby channels? particularly for the center dialogue channel? was this done using vegas or something?

I ask because I think splicing and mixing the new 5.1DVD ac3 in relation to the original stuff might be too much work, but it doesn't mean I can't pinch elements of it. however if we can take the PCM, and turn it into at least a reasonable surround track AC3 with a seperate dialogue centre channel that would be a big improvement."


2.0 to 5.1 Pro-logic.

Vegas was used simply to recombine the 5 WAVs into an AC3 file.

Here's a test I did, taking the Jaws AC3 file and panning some of the sounds from one speaker to another. It's subtle, but it's there (again, unless you have a 5.1 system, don't bother.)

I was working on a similar file, where all the speakers rotated around in circles, but I apparently never finished it, and deleted the files. Maybe I'll redo it tonight. It was pretty cool at the time.

<span class=“Italics”>MeBeJedi: Sadly, I believe the prequels are beyond repair.
<span class=“Bold”>JediRandy: They’re certainly beyond any repair you’re capable of making.</span></span>

<span class=“Italics”>MeBeJedi: You aren’t one of us.
<span class=“Bold”>Go-Mer-Tonic: I can’t say I find that very disappointing.</span></span>

<span class=“Italics”>JediRandy: I won’t suck as much as a fan edit.</span>