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Topic: Dolby Pro Logic II (Read 14238 times) previous topic - next topic
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Dolby Pro Logic II

Reply #25 –
Split thread.

Dolby Pro Logic II

Reply #26 –
Quote
But I believe that the argument was about using Dolby Pro Logic II to recover the surround sound information in the recording.

Yes. He will not be able to get surround sound like from a DVD. Dolby Pro Logic will get him a somewhat more spatial effect that he may or may not like. Again, that is exactly what was said in the first post.

Dolby Pro Logic II

Reply #27 –
I have to agree with saun97. According to Dolby Labs, their system will generate surround sound even if there was none encoded. They don't say anything about how "valid" is that surround information. They just say that it is generated, possibly using some tricks to give the impression of surround sound.

The point is, what is surround sound for you? Only the one that was encoded at the music? Or also other extra channels that can be generated artificially from the original music?

Dolby Pro Logic II

Reply #28 –
Quote
Hey Boojum

You understand, good man. Nodoubt audiophile material B)

But I'm not sure you understand. Binaural recorded surround recordings which only works with headphones are totally different than Dolby Pro Logic II decoding...
Garf split the thread, binaural discussion continues here.
Juha Laaksonheimo

Dolby Pro Logic II

Reply #29 –
Quote
According to Dolby Labs, their system will generate surround sound even if there was none encoded.

Nobody denied that. Heck, there are millions of DSP plugins which also create "surround sound".
Juha Laaksonheimo

Dolby Pro Logic II

Reply #30 –
Quote
I have to agree with saun97. According to Dolby Labs, their system will generate surround sound even if there was none encoded. They don't say anything about how "valid" is that surround information. They just say that it is generated, possibly using some tricks to give the impression of surround sound.

The point is, what is surround sound for you? Only the one that was encoded at the music? Or also other extra channels that can be generated artificially from the original music?

This is exactly what rc55 said, and what saun97 said was wrong. Funny how one can twist the issue afterwards huh?

Dolby Pro Logic II

Reply #31 –
Quote
a movie say that has a stereo track

Which, in all likelyhood, is DPL or DPLII encoded. One cannot be too sure, unless there's a handy Dolby logo somewhere on the packaging, or mention of DPL in the audio track settings. (DVD)

Dolby Pro Logic II

Reply #32 –
Quote
This is exactly what rc55 said, and what saun97 said was wrong.

I don't think so, sorry.

rc55 said:

"You can't add surround detail if it isn't there ... unless you have the "poor man" solution (i.e. a small delay between the front and rear speakers). Pro Logic II has positioning information embedded in the bitstream."

Whilst saun97 and Dolby say that you can have surround information even if there's none encoded. They don't say how, or what type, but they say they can.

Dolby Pro Logic II

Reply #33 –
saun97,

"Super confident aren't we? I suggest that before dispensing your advice you check your facts, or if you don't know just say say nothing. It is damaging to the nature of the Internet to have garbage floating around. I also believe that what you have done is far more discourteous to users of this site than to have poor linguistic skills!"

^^ That was your flame! Why are you being so selective with what you're trying to say? I was making a valid point, and my advice I had given was pretty much valid. Should I have been a bit verbose with my reply?

Essentially the matrix system is interesting, but I'm still valid with my argument is that you cant compare a genuine authored surround stream to a surround effected 2 channel stream, and even with Dolby's super new technology they may have interesting enhancements, my argument is still valid.

Ruairi
rc55.com - nothing going on

Dolby Pro Logic II

Reply #34 –
Quote
rc55 said:

"You can't add surround detail if it isn't there ... unless you have the "poor man" solution (i.e. a small delay between the front and rear speakers). Pro Logic II has positioning information embedded in the bitstream."

Whilst saun97 and Dolby say that you can have surround information even if there's none encoded. They don't say how, or what type, but they say they can.

(quote edited for emphasis)

I read it as rc55 saying that you cannot have the original surround details, but you can emulate them (poor man solution, for example with a delay or phase shift or a complex combination of both, which is likely exactly what Dolby does).

saun97 disagreed with this quoting the Dolby website, which implies he thinks Dolby Pro Logic can magically regenerate those details.

Illustrative quotes:

Quote
Quote from Dolby's website
"Dolby Pro Logic II is an advanced matrix decoder that derives five-channel surround (Left, Center, Right, Left Surround, and Right Surround) from any stereo program material, whether or not it has been specifically Dolby Surround encoded"


There is a very important difference in accuracy between a track with or without this information. The way this was quoted (with emphasis) makes it clear the difference was not understood by the quoter.

Also I said

Quote
Please explain to us. You have two stereo channels. How do you make 2=5, without, as rc55 said, using tricks to simulate the surround effect. Since it's mathemathically impossible, I really look forward to your argument.


It was clearly implied here that the '2' did not have any surround information added.
Note the 'tricks to simulate the surround effect'. This was 'refuted' by:

Quote
It IS mathematically possible through a technique (matrixing) developed for the original Dolby Pro-Logic, and now extended for the new Dolby Pro-Logic II. A simple example of this is the following. A recording of a person speaking. If the person is presented in the centre of the sound stage (ie the voice comming out of both speakers exactly the same), it is possible to determine that the voice should come out of only the centre channel. A simlar operation is applicable for the surround information with subtraction being performed between left and right channels.


Which, as I explained, can't be guaranteed to work correctly without additional information.

Furthermore, the attempt to refute my statement that 'it isn't possible without using tricks to simulate the effect' also illustrates he believes it could be done without tricks.

Need I go on? This thread is silly enough as it stands now.

Dolby Pro Logic II

Reply #35 –
Garf,

I don't think you do but if the flaming continues, I'm going to ask for this thread to be locked and edited so the useful information remains.

Thank you for being verbose and substantiating intelligently.

Ruairi
rc55.com - nothing going on

Dolby Pro Logic II

Reply #36 –
HI Garf

Two questions.

1. You carry on mentioning
Quote
this information
that is encoded into Dolby Surround tracks. You therefore must know what this is and how it was encoded. Would you please provide an explanation of this.

2. Do you consider proven mathematical techniques as mere 'tricks'

Dolby Pro Logic II

Reply #37 –
Quote
Quote

A recording of a person speaking. If the person is presented in the centre of the sound stage (ie the voice comming out of both speakers exactly the same), it is possible to determine that the voice should come out of only the centre channel. A simlar operation is applicable for the surround information with subtraction being performed between left and right channels.


This illustrates exactly why it doesn't work

There is nothing that says the sound should be in the center channel. It could just as well have been mixed so you were supposed to hear the same sound twice, once on the extreme right and once on the extreme left. You can't know which is correct unless that information is encoded!

as was stated, a sound that is the same in both channels is supposed sound like it's in the center, and that's exactly why it will be played back in the center channel speaker of a DPLII system.  It doesn't matter if the source material was made with DPLII in mind or not.  The simple fact that both the L and R channels of the source material contain the same information is what dictates that it's supposed to come from the middle.  If the L signal somehow differed from the R signal then it would be possible that it won't come from the center.  But in the case mentioned the sounds in both channels are the same, and there isn't any additional information necessary to glean that information.  Everything you need to know that is there in the L and R signals.  I don't know why you don't understand that.  It seems to me like you think there's actually some digital information in DPL or DPLII signals that state where sound A and sound B are supposed to be located, at least from how you're arguing it anyways.  And that is both unnecessary and not how it works.  I haven't read anything about how DPLII differs from DPL, but at least with DPL it's simply phase and similarity/difference that dictates where any given sound goes, which speaker(s) it gets played from.  There isn't any instructions embedded in the sound, other than the actual sounds themselves.

Dolby Pro Logic II

Reply #38 –
Quote
There isn't any instructions embedded in the sound, other than the actual sounds themselves.

http://www.dolby.com/tech/l.wh.0007.PLIIops.html
Quote
There are well-known characteristic differences between movie soundtracks and music recordings. For example, movies (and Dolby Surround TV shows) are mixed and monitored in a calibrated multichannel environment, so the desired end result when listening at home can be obtained from a similarly calibrated home theater system.

Stereo music, on the other hand, is not monitored through a surround system when being mixed, so it is not really known at that time how it will sound when played on a surround system.

For these reasons, the Movie mode of Pro Logic II has preset characteristics to ensure consistent results.

The Music mode, however, can be user-adjustable, assuming the decoder manufacturer decides to offer any of the following three optional controls. These controls are useful in any kind of decoder to allow optimization of the soundfield as desired, but are especially effective in automotive applications due to seating and speaker positions.
Juha Laaksonheimo

Dolby Pro Logic II

Reply #39 –
hmm, I don't see how that relates to the quote.

Dolby Pro Logic II

Reply #40 –
No need to lock from my part. I think it is clear what both sides intend to say, so no more discussion from my part. The trick is what you consider "surround information", an that we don't know how Dolby "recreates" this surround info when there's none encoded on purpose.

Aside from this, I think saun97 was probably too harsh in his response to rc55.

Dolby Pro Logic II

Reply #41 –
Quote
hmm, I don't see how that relates to the quote.

It relates in that way that the sound can have specific phase/signaling information/instructions created with DPL encoder/mixer which the DPL-II decoder uses to construct the wanted detailed surround sound.

If you have not done any pre-processing, as the text says "it is not really known at that time how it will sound when played on a surround system. "
Juha Laaksonheimo

Dolby Pro Logic II

Reply #42 –
so basically you repeated what I just said

Dolby Pro Logic II

Reply #43 –
Quote
so basically you repeated what I just said

Good. But perhaps you didn't understand that it was also what Garf and rc55 were saying, that unless there's specific pre-processing, it's not known how it will exactly sound..
Juha Laaksonheimo

Dolby Pro Logic II

Reply #44 –
well, actually, Garf said that a person talking, reproduced with a stereo signal with the same sound in both channels, shouldn't necessarily be reproduced by the center channel speaker in a DPLII setup.  Obviously, it should be reproduced by the center channel speaker since both the L and R channels contain the same information.  So I tried to correct him.  And then it seemed to me that you thought I was wrong and you were trying to correct me.  Only thing is, it seemed you were trying to correct me by stating I was correct, so that made no sense to me.

edit: typed though instead of thought

Dolby Pro Logic II

Reply #45 –
No, you didn't understand what I meant at all.

(I realize the example may look silly, but this effect is not that uncommon and I didn't have any more inspiration)

Imagine the real environment. I want to record the illusion that I'm shouting into your left and right ear at the same time, as if my twin brother were standing on the other side of you and shouting together with me.

Ideally, when played back on a surround sound system the illusion is preserved by panning the signal wide out to the sides and playing back equally loud front and back.

When you record it, you'll have exactly the same signal right and left. According to you this should be played back through the center speaker only. But that's the opposite of what we want!

You can only guarantee that you'll play it back the correct way by storing additional information.

Clear?

Dolby Pro Logic II

Reply #46 –
Quote
2. Do you consider proven mathematical techniques as mere 'tricks'

I will explain by example so maybe you understand it:

1) You encode a track with FLAC.

2) You encode a track with 64kbps MP3 Pro.

You can play them back, and they will both contain high frequencies. One of them has the original high frequencies, the other is using tricks to simulate the original, and may or may not sound well.

SBR is a 'proven' mathematical technique, but it's a 'trick' to reconstruct something that looks like the original frequencies

Dolby Pro Logic II

Reply #47 –
Garf, I understand what you're saying just fine.  Only thing is, that wasn't what was originally being discussed.  What was being discussed was the sound of a single person in the center of the soundstage, that is, with the EXACT SAME SOUND in both left and right channels.  That person is supposed to sound like they're in the middle.  And with the exact same sound information in both left and right stereo channels, that's exactly how it would sound.  And that's the exact scenario where a DPLII system should make that sound play from the center channel speaker.  That's also what happens if you try it, playback a stereo signal that contains the same info in both channels, and it comes out the center speaker. Just as it should. Clear?  What you're now talking about is not the same information in both channels.  If you did have a twin brother and you were both standing on either side of me shouting into my ear, it would not be the same information.  Both of you would have your own voice and timing differences, and it would sound like you were both at my sides rather than in the middle of my head.  It seems to me like you're trying to say when I sit in front of my speakers, halfway between each of them, and listen to a mono signal, it isn't going to sound like it's in the middle of the speakers, when in fact that's exactly what it's going to sound like.

Dolby Pro Logic II

Reply #48 –
Quote
Both of you would have your own voice and timing differences,

You are right, I forgot about this.

This means the reconstruction would be quite a bit more accurate than I thought, though the original point still stands, namely that a correct reconstruction can't be guaranteed unless the source was DPL to begin with, and not a track edited to cather to a standard hifi setup.

Thanks for providing a constructive argument.

Dolby Pro Logic II

Reply #49 –
in this specific case, yeah, with what amounts to a mono signal.  But that's the only point I wanted to confirm.  You're quite right about the other scenarios, hope I didn't sound like I thought you were wrong there.