Talk:Dolby Pro Logic

Last edit and my removal
The fact that Pro-Logic IIx can make 6.1 and 7.1 channel audio from "smaller" sources is already noted in the description. IIx is not a replacment for the EX codec. - Flash-Gordon 08:10, 5 Jun 2005 (UTC)

I am curious as to if there are any articles on Wikipedia as of yet that are related to the subject of "servo circuts"? They are an intregal part of the DPL II system, but not many may understand the influence and effect of the chips, or how they work. - -Ritz 18:25, 13 Jun 2005 (UTC)

Not that I'm aware of, but you can create one. Please feel free to add a bit about the circuits to this article, just be careful to keep it brief, because the focus of this page is the codec, not tha hardware that makes it work. —Preceding unsigned comment added by Flash-Gordon (talk • contribs) 02:52, 10 July 2005

Matrices
What the nun-sandwich do those numbers in the matrices mean? Are they a measure of the discreteness of each decoded channel(with 1.0 being a fully discrete channel), or are they some kind of reference as to where in the matrixed audo each channel can be found? boffy_b 01:25, 8 January 2006 (UTC)

They are relative signal levels.

The Pro Logic II "matrix"
Assume that a full-scale, 100%, 0dB signal is 1 volt.

If you want to send a 0dB signal to the left channel, you send a 1 volt signal to the left channel only, nothing to the right.

If you want to send a 0dB signal to the center channel, you send identical in-phase 0.707 volt signals to both left and right channels.

If you want to send a -6dB signal (50%) to the center, you send identical in-phase 0.354 volt signals to both left and right channels.

If you want to send a 0dB signal to the right-rear, you send a 0.8196 volt signal to the right, and the same signal to the left, but 180 degrees out-of-phase and decreased to 0.5774 volts.

Note that the rear-channel 180 degree phase shift is actually achieved by applying a +90 degree phase shift to the right rear, and a -90 degree phase shift to the left rear.

Pro Logic II decoding and "steering"
When a signal is present only in the right channel, it is routed to the right front.

When a signal is present only in the left channel it is routed to the left front.

When identical in-phase signals are present in both channels, the audio is routed to the center.

When identical, but out-of-phase signals are present in the left and right, the audio is routed to the rear speakers. If the out-of-phase signals have different levels, the audio is routed to the dominate channel.

When there is a mix of the above conditions, the steering effect may reduced or turned- off completely. --DougDbug 01:38, 25 May 2006 (UTC)

Automatic detection
Some receivers can automatically switch on their DPLII decoder only if they detect a DPLII signal from the source. How does this detection work? Balfa 18:33, 27 September 2006 (UTC)
 * (bump) Good question, as Dolby Surround tracks don't carry a discrete "flag" like DD and DTS do. Most receivers that I've worked with will switch to a user-preselected decode mode based on the number/type of inputs the source is sending. E.g., optical/coaxial digital, the receiver will switch to DD or DTS as appropriate ... analog, 2-ch input, receiver switches to PL, PLII Movie, PLII Music, PLIIx Movie, blah blah blah. Just my guess. YMMV. --~D BS Talk / Contribs 20:58, 24 November 2006 (UTC)
 * Well, my old amp (a cheap Amphion Mediaworks) used to turn on DD/DTS when necessary (straightforward to do) but if I gave it a standard analogue stereo signal, it would either leave it unprocessed or pass it through its DPLII processor, based on... something. Of course I could override it to always use DPLII or always bypass DPLII in the settings, but it was this "Auto Detect" option that has me confused. Balfa 18:46, 11 December 2006 (UTC)


 * Maybe stereophonic and monophonic programming? Easy enough for a receiver to switch on that. I just played with a low-end Sony, and it had an A.F.D. mode which auto'changed, ... pretty much DD or DTS for those (coaxial, digital) inputs, then PLII for stereo analog. Didn't try mono sources. David Spalding ( ☎ ✉ ✍  ) 20:09, 11 December 2006 (UTC)

First use of Pro Logic
I have a memory that the first film to use Pro Logic was a remake of the Jazz Singer - which, of course, would have a nice symmetry, could someone confirm or deny that? What was the first film to be encoded with Pro Logic (presumably the first surround sound system)? -- Apepper 20:53, 17 December 2006 (UTC)


 * Are you talking about in the theatre, or home video release? BTW, Dolby Pro Logic refers to the decoding circuitry, not a media encoding. Perhaps the first paragraphs of the article will answer your question. -- David Spalding ( ☎ ✉ ✍  ) 22:41, 17 December 2006 (UTC) updated 22:43, 17 December 2006 (UTC)


 * It was really the first cinema release I was interested in; if it was in 1976 then its too early for the Jazz Singer. It may not be the right article, but I'd be interested to know about the impact of the surround sound systems on cinemas who, presumably, had to make a fairly major investment to equip for surround sound.Apepper 23:25, 17 December 2006 (UTC)

Pro Logic encoding matrix?
The Dolby Pro Logic Encoding Matrix table appears to have five channels. I thought that Dolby Pro Logic was a four-channel format, and that five channels were not added until Pro Logic II? Am I confused and do I misread the article text? jhawkinson 05:00, 18 May 2007 (UTC)

The back channels both have the same information, but are considered separate channels on the standard. So on the matrix you have Surround Left and Surround Right, but the data is exactly the same, actually the same as in Dolby Surround. Ricnun 08:19, 18 May 2007 (UTC)


 * But the article states it's an encoding matrix, and only one surround channel is encoded. Listing two surround channels for Pro Logic is confusing. I am with jhawkinson on this. It should be changed. 216.123.197.25 23:54, 20 July 2007 (UTC)


 * I was satisfied with Ricnun's explanation. jhawkinson 02:28, 21 July 2007 (UTC)

Image copyright problem with Image:Dolby surround.jpg
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Where is the matrix of Dolby Pro Logic IIz ??
I saw the matrix rules about Dolby Pro Logic II but where is the IIx and the IIz please ? In what manner do they are coded ? What are the VST, Plug-Ins, Stand alone programs that are capable to ENCODE 9.1 channels in 2 ? ( Pro Logic IIz ) or 7.1 channels in 2 ? ( Pro Logic IIx ) ?

Thank you very much Iw2mln (talk) 11:52, 22 December 2009 (UTC)


 * Nobody answered so that I investigated and found the answer directly with Dolby Labs. The extra channels in Dolby Pro Logic IIx and IIz are NOT discrete channels. I mean: they are not encoded. Those channels are onlyextrapolation of not correlated signals, that are sent to extra 2 back channels in IIx and 4 extra channels ( 2 back-side and two Upper-front ) in IIz. —Preceding unsigned comment added by Iw2mln (talk • contribs) 17:35, 8 February 2010 (UTC)

Software encoder
The article states that liba52 and HandBrake provide a DPL compatible downmix, which I think is incorrect and highly misleading statement. If you check the source code, neither project implements a Hilbert transformer (the rotation by the complex j, which is indicated in the matrix just a few sections above), and this is needed to avoid center to rear signals pan over to the left. See also a discussion at Doom9:, which cites the requirement in Dolby Labs' manual. – Ylai (talk) 02:43, 25 July 2010 (UTC)

Source of the DPLII encoding matrix?
I wonder where are the Ls, Rs to Lt, Rt DPLII encoding coefficients (for the 5.1 downmix) coming from? Is there a reliable source from Dolby Labs where they can be checked against?

From the DP563 Dolby Pro Logic II and Surround Encoder Quick Start Guide and Xbox 360 Audio Mixing and Monitoring Best Practices (Word format), the DPLII attenuation for the stereo surround channels are given as -1.2 dB and -6.2 dB. Due to rounding, 0.489779² + 0.870964² = 0.998462, which suggests that a unitary normalization is desired.

Combining the two attenuation into an angle is therefore the better approach to deduce the exact form. To obtain a rounded value that matches (-1.2 dB, -6.2 dB), 29°.1414 ≈ 0.508614 < φ < 0.515082 ≈ 29°.512. This is suggestive that the attenuation is not expressed trigonometrically using some exact angles.

Now take φ = tan-1(0.489779/0.870964) ≈ 0.512269. Expanding sin²(φ) as continued fractions gives the sequence


 * $$\left( 0,\; \frac{1}{4},\; \frac{6}{25},\; \frac{37}{154},\; \ldots\right)$$

(with the third value roughly corresponding to the two digit significant figures in the manual). So it appears that when expressed in rectangular coordinates, Dolby is using something that is, or is very close to:


 * $$\left( \pm j\frac{\sqrt{19}}{5}, \; \pm j\frac{\sqrt{6}}{5} \right)$$

or (-1.19186 dB, -6.19789 dB), i.e. matching well the rounded decibel values.

Here someone tested several coefficients, and obtained as result what corresponds to the second value in the continued fraction expansion above. However, the corresponding (-1.2 dB, -6.0 dB) would seemingly contradict both documents.

– Ylai (talk) 15:15, 30 July 2010 (UTC)

Pro Logic II Game
Google took me here when searching for "Pro Logic II Game" but the one line sentence on Game mode doesn't really tell how Game mode works and how it's different from Music or Movie, just that it's for video games and featured on some gaming consoles. A bit vague? Could this be expanded more? Perhaps into it's own section, along with Movie & Music modes? Music mode has many options such as Panorama mode which is not discussed at all. 173.52.78.210 (talk) 02:40, 30 August 2011 (UTC)

The only thing I could find on Game mode was "game mode is identical to movie mode, but it directs all bass information to the sub-out, while movie mode just directs bass from the front channels" not a reputable source though. 173.52.78.210 (talk) 03:03, 30 August 2011 (UTC)

Mathematical definition of matrix
It is not clear from the article what mathematical operation is represented by the phase shift. If you have any comments, please discuss this on Talk:Matrix decoder. Han-Kwang (t) 22:46, 23 May 2012 (UTC)

New Logo for Dolby Pro Logic II
I know that at first Dolby Pro Logic II was in the market going by "Dolby Surround Pro Logic II", but now it goes by straight "Dolby Pro Logic II". According to the official site of Dolby Pro Logic II, it has a new logo now, and I have already remade it into vector format. Am I going to upload to File:Dolby-Surround-Pro-Logic-II.svg, or upload to Dolby-Pro-Logic-II.svg? The first file name is very misleading.Timothy Gu (talk) 19:12, 21 December 2012 (UTC)

DPL II from Dolby Digital 5.1 - does that make sense?
»The extra channel content is extracted using the difference between the spatial audio content between two individual channels of stereo tracks or Dolby Digital encoded 5.1 channel tracks and outputs it appropriately.«

Not an expert, just a bypassing reader here … but does that make sense, to derive DPL II from Dolby Digital 5.1? I wouldn't have thought so. Why derive five channels if you already have five plus one? Did the author mean DPL II is derived from Dolby Digital 2.0, not 5.1? — Preceding unsigned comment added by 85.179.214.26 (talk) 15:55, 11 March 2013 (UTC)

DPLII does 5->2->5, it can take Dolby Digital, matrix encode that into a stereo file - with the surround channels encoded phase-shifted, and then a decoder can take that stereo track and upmix it to 5 speakers using the phase information. 176.24.117.227 (talk) 21:07, 15 March 2014 (UTC)

Old logo missing from article!
Where is the old logo? It is missing from the article and should be added as soon as possible in vector format. Here's a reminder how it looked like: http://imageshack.com/scaled/large/600/7pp.gif -- Alexey Topol (talk) 23:06, 21 October 2013 (UTC)

Why are digital methods also being presented?
The title of this article is "Dolby Pro Logic". Why are digital methods also being presented? Is the intention to confuse readers? --24.166.91.73 (talk) 16:22, 5 May 2015 (UTC)

Reorganization
Reorganized the information to focus on the topic: Dolby Pro Logic decoding. So removed all talk of digital surround (other than a mention to current day software or hardware that outputs DPL compatible LtRt tracks). Still some redundant mentions to Dolby Surround as encoding and decoding techniques, etc, but it's a clearer article I think. 4throck (talk) 23:49, 6 November 2016 (UTC)

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Clarification of opening paragraphs
The opening paragraphs appear to be ambiguous or contradictory:
 * Dolby Sound "was adapted for home use in 1982 as Dolby Surround".
 * Dolby Sound "was replaced by the improved Pro-Logic system in 1987".
 * "The term "Dolby Surround" describes the encoding technology or matrix-encoded soundtrack, whereas Pro Logic refers to the decoding technology and processor."

Did Dolby Prologic replace Dolby Sound, or do the two technologies work together (with Dolby Surround referring to the encoding, and Pro Logic referring to the decoding)? Ubtree (talk) 11:12, 13 February 2019 (UTC)

technical details obfuscated
for my liking, there's nowhere near enough maths in the article, explaining how the matrixing works. I was taught a great deal about the workings of the various "quadraphonic" systems that emerged in the 70s, & this article touches on them just enough to raise a suspicion that there's a technical overlap that dolby would prefer we didn't examine too closely. I'll have to do some research into the various patents, but the involvement of jim fosgate in both technologies caused a raised eyebrow here. basic dolby pro-logic is nothing more than hafler effect, pulling a false surround channel from the stereo pair. the later developments, as described here seem to resemble the techniques used in SQ quad processing. any & all of these systems were in any case made redundant the minute it became possible to distribute discrete channels properly (i.e. digitally, for the most part) & only exist now as legacy technology, or to create false surround channels from stereo. this latter, deriving or synthesizing surround information from stereo, is where I feel that the article loses focus, for the reasons above- there is a lot of overlap between the techniques marketed as dolby technology, & the SQ decoding used in quad systems. duncanrmi (talk) 09:18, 28 July 2023 (UTC)