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Topic: Dolby Pro Logic II (Read 14237 times) previous topic - next topic
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Dolby Pro Logic II

Reply #50 –
Hey Garf

Here is a 'trick' for you

You have the information of a projectile's displacement against time. With a mathematical 'trick' of differentiation we can reconstruct the projectile's original acceleration against time. It might or might not be 100% the original acceleration against time however, there is a mathematical proof to show that it always is which I have not actualy verified for myself.

Just because we havn't studied, or have a name for a mathematical operation, doesn't mean that it's a 'trick' or a 'miracle'. My little brother thinks long division is a 'trick'.

Your example of Twins----
OK you see the point (Thanx Shorty)
This example disturbs me though, do people shout at you often? 

If you look at most recordings, even though they are not specificaly encoded, they do contain cues as to positioning information. As an example take a look a live concert with the artists facing the crowd. The sound of the crowd is recorded from the opposite side of the mikes, and will sound different than when you record a crowd with the mikes facing it. If you play this recording back on a Pro-Logic system, you will hear the recording as if you were at microphone position. with the crowd behind you.

Quote
reconstruction can't be guaranteed unless the source was DPL to begin with


(Please note that DPL / DPLII are decoding systems. No source is ever encoded with DPL / DPLII, but reather with Dolby Surround. You will never see a DPL / DPLII sign on any source material.)

Furthermore you imply that reconstruction is guaranteed if source is Surround encoded, this is not quite correct because of the way DPL extracts information for its various channels. This is very simplisticly as follows.

Surround = Ks * (LC - RC)
This is Low Passed at 8Khz

Centre = Kc * (LC + RC)
This quadruples the power for the spectrum present in both channels. Once this is re-normalised the information is attenuated even further.

Right = RC - Surround - Centre
Left = LC - Surround - Centre

where
K? = channel matrix co-efficient
LC = Left Channel signal
RC = Right Channel signal

To activate surround channels, the signal between left and right must be different, so Dolby phase shifts the signal that is required to be played in the surround speakers. One one channel it is phase shifted forward 90Degrees on the other the signal is shifted backward 90Degrees. When these two signals are subtracted, they are 180 Degrees out of phase which causes the signal to be full restored. This is the attenuated via matrix co-efficent, and also delayed by 15 - 20 ms.

The point is that what if that was what the way the engineer intended the signal to sound like anyway through the front left and right channels?

Dolby Pro Logic II

Reply #51 –
Quote
Just because we havn't studied, or have a name for a mathematical operation, doesn't mean that it's a 'trick' or a 'miracle'. My little brother thinks long division is a 'trick'.


Your brothers long division (assuming he didn't mess up) will produce an exact and correct answer. So it isn't a 'trick' in this context.

SBR has sound mathemathical groundings that are fairly well understood, but it's a 'trick' because it takes guesses to reconstruct the original sound (and is sometimes wrong).

Quote
Furthermore you imply that reconstruction is guaranteed if source is Surround encoded, this is not quite correct because of the way DPL extracts information for its various channels. This is very simplisticly as follows.
[blabla]
The point is that what if that was what the way the engineer intended the signal to sound like anyway through the front left and right channels?


JohnV already pointed out this is false, because a surround encoded track is produced in monitored conditions to guarantee what comes out the customers setup is exactly the same as what came out in the producing studio.

Next you point out that it's not possible to store all possible sounds/spatial configurations on a surround track, which is a point that has already been made several times throughout this thread by other people.

So, on one side you are arguing you can always get the correct reconstruction from a standard stereo track, on the other side you are arguing that you can't get guaranteed correct reconstructions out of a surround encoded track.

Dolby Pro Logic II

Reply #52 –
Correct and if you agree with them why do you keep on perporting otherwise?

Dolby Pro Logic II

Reply #53 –
Not True Garf

I am saying that it is possible to decode "surround information". Where have I, or Dolby said that it will be accurate?

THe definition of Trick that I beleive you refer to is "An act or procedure intended to achieve an end by deceptive or fraudulent means". Well as long as the system is not sold as being accurate this is not true.

Dolby Pro Logic II

Reply #54 –
Quote
Correct and if you agree with them why do you keep on perporting otherwise?

Quote
Not True Garf


You sure change opinion quickly :)

I'll state my claims:

1) a normal stereo track cannot be guaranteed to be correctly dematrixed into the original soundfield, because it was (re)mixed to sound good on a standard stereo (and thus doesn't preserve the original information. I had a misunderstanding here, which _Shorty cleared up)

2) a surround sound encoded track will have the exact soundfield the producing engineer intended, because a) it encodes the surround positioning information b) the playback and producing conditions are standardized

The original statement was:

Quote
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.


Which my claims agree with.

I have no idea what you claim since it seems to change every 2 posts, but it can't be my claims since you flamed the person making the quoted statement.

Dolby Pro Logic II

Reply #55 –
Quote
"the playback and producing conditions are standardized


Realy? So when I playback a track in a room of 5x5 meters it will sound the same as if I played back that track in a room of 20 x 20 meters. Or if I play back a track in a carpeted room, it will sound the same as if I played the sound back in a tilled room. All in terms of spatial localization of course?

I think not?

I say that you can extract surround information from a stream. Wether or not it is the original surround intended is not in question as any 2 channel source will not be accurate

Dolby Pro Logic II

Reply #56 –
Quote
Quote
Correct and if you agree with them why do you keep on perporting otherwise?


Quote
Not True Garf




You sure change opinion quickly


Caused by your editing 

"Not true" relates to

Quote
So, on one side ....


"Correct" relates to

Quote
Next you point out


[span style='font-size:14pt;line-height:100%']PS you have ignored my question
Where have I, or Dolby said that it will be accurate?[/span]

Dolby Pro Logic II

Reply #57 –
Quote
"Not true" relates to

Quote
So, on one side ....


"Correct" relates to

Quote
Next you point out



Thanks, at least that is clear now.

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[span style='font-size:14pt;line-height:100%']PS you have ignored my question
Where have I, or Dolby said that it will be accurate?[/span]


[span style='font-size:5pt;line-height:100%']
I repeat: I have NO idea WHAT you are saying or claiming!
[/span]

Dolby Pro Logic II

Reply #58 –
I almost missed your reply on my 1400x1050 Res Screen 

This is a simple question to answer Garf. I dont see why you have a problem understanding it

"Where have I, or Dolby said that it will be accurate?"

You are avoiding the issue

Dolby Pro Logic II

Reply #59 –
Quote
I almost missed your reply on my 1400x1050 Res Screen  :D

This is a simple question to answer Garf. I dont see why you have a problem understanding it

"Where have I, or Dolby said that it will be accurate?"

You are avoiding the issue

For the third time: I have NO idea WHAT you are saying or claiming exactly!

But since this is avoiding the issue in your eyes, I'll quote:

Quote
Quote

I'm saying that no decoder can reconstruct the correct stereo/surround image if that information was not encoded.

Ahh Garf
Dolby Labs disagrees, as do I. It is not meant to recreate the sound as it was exactly (that is impossible for any decoder including Dolby Digital EX decoders) but rather provide a reasonable experience of it. The reasons for this are varied but include things such as room acoustics, Loudspeaker Frequency response etc. Lucasfilms has tried to address this with their THX specification, but it still does not perfectly correct the situation.


So, here I say that the correct image cannot be reconstructed, and you disagree, which implies you think it can. I think that is saying that it would be accurate. What you say afterwards doesn't actually disagree with what I said, which makes me believe we're just confused about what the other is claiming. I've stated what I claim, but you're refusing to state what you claim. We cannot have a constructive argument this way!

I'll restate my claims:

1) a normal stereo track cannot be guaranteed to be correctly dematrixed into the original soundfield, because it was (re)mixed to sound good on a standard stereo (and thus doesn't preserve the original information. I had a misunderstanding here, which _Shorty cleared up)

2) a surround sound encoded track will have the exact soundfield the producing engineer intended, because a) it encodes the surround positioning information b) the playback and producing conditions are standardized

You can read both as having the amendement 'or at least as correct as practical playback circumstances permit'.

My main point is that surround encoded recording will have much more correct spatial image than a normal encoding on playback through a DPL system. Agree or disagree?

Dolby Pro Logic II

Reply #60 –
I agree fully with this

The initial question in this thread was from a user (I won't quote his exact words lest, rc55 comes down on my head from a linguistic point of view, but will rather summarise what he wanted.) who wanted to have something similar to the function Dolby Prologic II  function on Windvd. He was already happy with the 'surround' information that he was getting with that (remember WindDVD also play MP3's etc). Wether the surround is accurate or not is not in question, but rather weather users find this acceptable.

Have you tried the filter from the link I submitted? http://matrix-mixer.sourceforge.net/

It is not a bad solution