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| Registered: March 13, 2007 |  Posts: 21,610 |
| | Posted: | | | | Well put, Mithi.
Skip | | | ASSUME NOTHING!!!!!!
CBE, MBE, MoA and proud of it.
Outta here
Billy Video |
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| Registered: June 22, 2007 | | Posts: 89 |
| | Posted: | | | | One explanation referring to matrixed Dolby tracks: There is no way to simply alter a matrixed Dolby soundtrack into a pure Stereo track. The only way would be to create a completely new mix of the film's bare soundtracks from scratch which a) would cost a lot of money and b) would make no sense at all.
Ergo any film that has a matrixed Surround soundtrack (no matter whether downmixed from 5.1 or originally mixed in matrixed 2.0) will stay in matrixed Surround mode when overlaid with an audio commentary.
Of course THE WIZARD OF OZ or other monaural films will not get a Surround soundtrack when being equipped with an audio commentary. I think MadAcid only wanted to point out that Surround does not become Stereo just because of the addition of an audio commentary. |
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| Registered: March 13, 2007 | | Posts: 2,759 |
| | Posted: | | | | Quoting madacid: Quote:
And even an additional mixdown to 2.0 again wouldn't eliminate the matrixed surround-sound (from the score in background). That's only true, if the original mix has been matrixed surround sound (Dolby Surround in home cinema or Dolby Stereo in the theatre). Discrete multi channel sound (5.1 or higher) can of course be mixed down to stereo easily. |
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| Registered: June 22, 2007 | | Posts: 89 |
| | Posted: | | | | How that??? Of course it can by only using the left and the right channel but then You lose a lot of information, mainly a big portion of the dialogue of the center track. And who would be so stupid? If You want to have all the five-channel information audible together with the audio commentary in 2.0 there is no other way as to use the matrixed 2.0 downmix. | | | | Last edited: by schaumi |
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| Registered: March 13, 2007 | | Posts: 2,759 |
| | Posted: | | | | Quoting schaumi: Quote:
How that??? Of course it can by only using the left and the right channel but then You lose a lot of information, mainly a big portion of the dialogue of the center track. And who would be so stupid? If You want to have all the five-channel information audible together with the audio commentary in 2.0 there is no other way as to use the matrixed 2.0 downmix. OK this gets technical now: Dolby Surround basically uses phase information for the matrix. Let's say the discrete channels are l (left), c (center), r (right), and s (surround, back). Then they get matrixed into L, R (left, right) the following way (simplified): L = l + sqrt(2) * c + sqrt(2) * j * s R = r + sqrt(2) * c + sqrt(2) * k * s where j is a +90 degree phase shift and k is a -90 degree phase shift. If you leave out the phase shift, you get a "flat" stereo mix: L = l + sqrt(2) * c + sqrt(2) * s R = r + sqrt(2) * c + sqrt(2) * s See Wikipedia for more details. |
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| Registered: March 13, 2007 | | Posts: 21,610 |
| | Posted: | | | | Watching Cass' eyes glaze over now.  Skip  | | | ASSUME NOTHING!!!!!!
CBE, MBE, MoA and proud of it.
Outta here
Billy Video |
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| Registered: May 26, 2007 | Reputation:  | | Posts: 2,879 |
| | Posted: | | | | Quoting skipnet50: Quote:
Watching Cass' eyes glaze over now.
Skip *glazed look*  *goes down* Not a technical person here. Reaping the benefits of a liberal arts education - ask me something about art, literature, culture, religion, history, literary and social theory - I'm your gal. But after two BAs and one MA, the pitiful tech stuff they tried to teach me for MS was not happening (of course, could have been the professor on that one, no one I know who took that class learned a darn thing). | | | If more of us valued food and cheer and song above hoarded gold, it would be a merrier world.
-- Thorin Oakenshield |
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| Registered: March 13, 2007 |  Posts: 302 |
| | Posted: | | | | Quoting schaumi: Quote:
... I think MadAcid only wanted to point out that Surround does not become Stereo just because of the addition of an audio commentary. Thx Schaumi, exactly this was my point  | | | regards, Mad -
My HD-Media, DVDs, Laserdiscs |
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| Registered: March 13, 2007 | | Posts: 302 |
| | Posted: | | | | Quoting RHo: Quote:
Quoting schaumi:
Quote:
How that??? Of course it can by only using the left and the right channel but then You lose a lot of information, mainly a big portion of the dialogue of the center track. And who would be so stupid? If You want to have all the five-channel information audible together with the audio commentary in 2.0 there is no other way as to use the matrixed 2.0 downmix.
OK this gets technical now:
Dolby Surround basically uses phase information for the matrix. Let's say the discrete channels are l (left), c (center), r (right), and s (surround, back). Then they get matrixed into L, R (left, right) the following way (simplified):
L = l + sqrt(2) * c + sqrt(2) * j * s
R = r + sqrt(2) * c + sqrt(2) * k * s
where j is a +90 degree phase shift and k is a -90 degree phase shift.
If you leave out the phase shift, you get a "flat" stereo mix:
L = l + sqrt(2) * c + sqrt(2) * s
R = r + sqrt(2) * c + sqrt(2) * s
See Wikipedia for more details. so what does this help now? Fact is:l if you mixdown a 5.1 mix to 2.0 it's still a Surround-Track.  | | | regards, Mad -
My HD-Media, DVDs, Laserdiscs |
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| Registered: March 13, 2007 | Reputation:  | | Posts: 2,217 |
| | Posted: | | | | Quoting madacid: Quote:
so what does this help now? Fact is:l if you mixdown a 5.1 mix to 2.0 it's still a Surround-Track. If you down mix them, sure. If you just throw away everything but left and right channel there is not a bit of surround left. The DD 5.1 has 6 discrete channels. (DD EX is devils work, doesn't count) So, as long as you don't know how exactly that commentary is mixed in, the "but the original track was surround" proves next to nothing, and I would rather trust what my DVD Player claims to send and what my AV-Receiver claims to receive. cya, Mithi | | | | Mithi's little XSLT tinkering - the power of XML --- DVD-Profiler Mini-Wiki | | | | Last edited: by Mithi |
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  | T!M | | Profiling since Dec. 2000 |
| Registered: March 13, 2007 | Reputation:  |  Posts: 8,736 |
| | Posted: | | | | Quoting Mithi: Quote:
So, as long as you don't know how exactly that commentary is mixed in, the "but the original track was surround" proves next to nothing, and I would rather trust what my DVD Player claims to send and what my AV-Receiver claims to receive. Agreed! |
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| Registered: March 13, 2007 | | Posts: 2,759 |
| | Posted: | | | | Quoting madacid: Quote:
Quoting RHo:
Quote:
OK this gets technical now:
Dolby Surround basically uses phase information for the matrix. Let's say the discrete channels are l (left), c (center), r (right), and s (surround, back). Then they get matrixed into L, R (left, right) the following way (simplified):
L = l + sqrt(2) * c + sqrt(2) * j * s
R = r + sqrt(2) * c + sqrt(2) * k * s
where j is a +90 degree phase shift and k is a -90 degree phase shift.
If you leave out the phase shift, you get a "flat" stereo mix:
L = l + sqrt(2) * c + sqrt(2) * s
R = r + sqrt(2) * c + sqrt(2) * s
See Wikipedia for more details.
so what does this help now? Fact is:l if you mixdown a 5.1 mix to 2.0 it's still a Surround-Track. If you'd have understood the formulas given, then you would know that there are several ways to downmix. At least one results in a 2.0 track which is not surround. |
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| Registered: March 13, 2007 | | Posts: 2,759 |
| | Posted: | | | | Quoting Mithi: Quote:
So, as long as you don't know how exactly that commentary is mixed in, the "but the original track was surround" proves next to nothing (...) If the original mix has been Dolby Surround (matrixed surround), then there is in fact no way to remove the matrixed surround info hidden in the phase info. In those cases the commentary really has to be surround as well. |
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| Registered: June 22, 2007 | | Posts: 89 |
| | Posted: | | | | Hi RHo!
You maybe right with Your formula but how do You leave out the phase shift? As You mentioned in Your final posting: "If the original mix has been Dolby Surround (matrixed surround), then there is in fact no way to remove the matrixed surround info hidden in the phase info."
But even if You could do so: Who needs a "flat stereo mix" under the audio commentary when it is much easier to take the already available matrixed Dolby Surround Mix? This mix is called SVA and has to be manufactured for any film to deliver a matrixed 4-channel-master for the optical analog soundtrack which has to go on every film print in addition to the digital sound. That exactly is what You find as a basis for the audio commentary tracks on DVDs (as long as the audio commentary track is in 2.0 and applies to feature films).
And concerning Your suggestion to take only the left and the right channel from the discrete 5.1 mix: I already mentioned earlier that in this case You will not only lose the surround information but first of all You'll have almost no dialogue audible under Your audio commentary. Can't be reasonable at all ... So You have to use a downmix anyway, right? | | | | Last edited: by schaumi |
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| Registered: March 13, 2007 | | Posts: 2,759 |
| | Posted: | | | | Quoting schaumi: Quote:
Hi RHo!
You maybe right with Your formula but how do You leave out the phase shift? As You mentioned in Your final posting: "If the original mix has been Dolby Surround (matrixed surround), then there is in fact no way to remove the matrixed surround info hidden in the phase info."
But even if You could do so: Who needs a "flat stereo mix" under the audio commentary when it is much easier to take the already available matrixed Dolby Surround Mix? This mix is called SVA and has to be manufactured for any film to deliver a matrixed 4-channel-master for the optical analog soundtrack which has to go on every film print in addition to the digital sound. That exactly is what You find as a basis for the audio commentary tracks on DVDs (as long as the audio commentary track is in 2.0 and applies to feature films).
And concerning Your suggestion to take only the left and the right channel from the discrete 5.1 mix: I already mentioned earlier that in this case You will not only lose the surround information but first of all You'll have almost no dialogue audible under Your audio commentary. Can't be reasonable at all ... So You have to use a downmix anyway, right? The formula only works for discrete channels. There is no phase shift involved there. And I have not suggested to leave out any channel from a 5.1 mix (that would have been you). I have suggested to use a similar method to mix down the 5.1 channels as I have shown it would be possible to mix down a discrete 4.0 mix. To sum it up again: an original matrixed Dolby surround mix can't be flattened to stereo, while a discrete multi channel mix can. That a studio would probably use the available matrixed surround mix as a basis for their commentary, I would not deny. But in principle they could easily create a real 2.0 stereo mix (without loosing dialogue or surround noises) or make a 2.0 mono down mix. In fact I could create a 2.0 stereo down mix of a 5.1 mix with my own equipment (a simple mixing desk), while I could not create the phase shift needed for a matrixed surround mix. | | | | Last edited: by RHo |
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