Talk:Dolby Pro Logic

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[edit] 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

[edit] 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)

[edit] 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. --~DBS 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)

[edit] 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)

[edit] 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)

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