Pro Logic IIx question

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Not true. Only from 2, 5 and 6 channel sources. 1,3 and 4 channel sources won't work.
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Well I don't think so because there is no such thing as Dolby DTS. Dolby is one company and DTS is a competing company.
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Ignoring the previous problems with your questions ... the sound from the fronts and center will be identical. The 2 sides wil be different since the correlated sound (ie mono component) will be extracted , processed and sent to the rears.


Ed

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Sorry. Edited for clarity. I am not familar with audio formats (as if you cannot tell).


Ok you say the sound is gonna be different on the 2 sides. Lets try to put it into a scenario


I am walking through the woods and all of a sudden here comes an enemy to my left--are his footsteps still going to come from the left speaker? Or I mean what is going to happen? Is it going to mess up the sound?

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Ed is correct: the sounds going to the side speakers will be different if you apply PLIIx.


First things first. When you apply PLIIx to 5.1 material, the front three channels are left untouched. 3 channels, 3 speakers; nothing to process. Each channel is simply routed to its respective speaker.


The processing actually occurs in the surround field, where 2 surround channels are steered over 4 surround speakers. The idea is pretty simple. If you were listening using only 2 surround speakers, sounds that are common to both surround channels would phantom image somewhere in the middle, giving the impression of being behind you.


The problem is that you have to be sitting in a narrow sweet spot exactly between the two surround speakers in order to hear the phantom rear image behind you. If you are off-axis, the phantom rear image will pull towards whichever surround speaker you are closest to.


PLIIx extracts sounds that would normally phantom image behind you and sends them to speakers physically located behind you. Since these are now hard sounds (not phantom images), they will no longer drift. So no matter where you're sitting, these sounds will always appear to come from the correct direction: behind you. As stanger89 pointed out, the original directionality hasn't really changed, but the imaging stability has been improved.


After sending those sounds to the rear speakers, the processing has to do one more thing: actively cancel those sounds from the side speakers. You don't want to hear those sounds from the wrong direction or the same sound from two different directions.


That's why the sides will sound different, because the rear info has been removed from those speakers. This won't mess up the surround field but instead will make rear-vs-side imaging clearer. Make sense?


Sanjay

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DAMN BRO YOU LAID IT OUT!



Seriously, I have not had an explanation that clear in a long time.


It seems like you did a great job of explaining this, now I have an understanding of what PLIIx does. But just to make sure, tell me if this is correct:


So my source is sending out info to the 2 sides that are supposed to create an effect to where if someone was coming up behind me, I would hear their footsteps behind me. This is the phantom image you were talking about. But instead of using a phantom image, PLIIx extracts the rear phantom image sounds from the sides and instead sends them to the rear speakers. Therefore all PLIIx does is extract the rear phantom image audio from the sides and sends it to the back.


How does PLIIx know which data is the rear phantom image? And is PLIIx a digital format?



Can you apply PLIIx to DTS or THX sources?


What if I send my receiver a THX format, which it does not claim to support?


What will happen if I have 6.1 channels of audio coming in and 7.1 speaker setup with and without PLIIx applied to it?

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Your understanding is correct. I already answered how that is done in post #2 - the correlated data between the L&R surrounds (i.e. the mono content) is sent to the back and removed from the sides. PLIIx is not a format. Its a process applied to formats.
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Some (better) receivers/pre pros allow application to DTS and some don't. The is no such thing as a THX source.
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Again no such thing , that's why your recevier makes no such claims.
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PLIIx will create a stereo back while otherwise the 2 back speakers will play mono.


Ed

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By where the energy of certain sounds are in the 2 surround channels.


Let's pretend that YOU are the PLIIx algorithm. You have 4 surround speakers laid out in a 180 degree arc in the back half of the room. You're given 2 channels of surround information and asked to place certain sounds in the appropriate speakers. What do you do?


Imagine a sound that starts in the left surround channel and slowly moves to the right surround channel. You would move that sound through each of the 4 speakers, one by one from left to right. Think about where the sound is between the channels and it will give you a good clue about which speaker it should go to.


When the sound is only in the left surround channel, you place it in the left side speaker. That's where you would have heard it anyway: all the way to the left. When the sound is mostly in the left surround channel and a little bit in the right surround channel, then you start moving it to the left rear speaker. That's where it would have imaged anyway: over your left shoulder. When the sound is equally loud in both surround channels, you send it to both rear speakers. That's where it would have imaged anyway: directly behind you. And so on, as you complete the arc all the way to the right side speaker (when the sound is only in the right surround channel).


Don't think of the 2 surround channels as two discrete pools of information to be sent to only 2 speakers. Think of the surround channels as a semi-circular road map, stretching from your left side all the way around to your right side. That semi-circle can be made up of 3 speakers or 4 speakers or 40 speakers; it doesn't matter. Where ever a particular sound is between those 2 channels will clue you in which speaker you should send that sound to. As sounds move from one channel to the other, they will pass through the appropriate speakers in a smooth arc.


It's not complicated. Just a dumb circuit that checks voltages to see where the energy of a dominant sound is (towards the left or right). Then it just sends it to the appropriate speaker in the arc and supresses that sound in all the other speakers (using a cancelation signal). That last part helps make directionality a little more clearer and precise sounding.
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All the processing is done in the digital domain. But, as Ed pointed out, it's not a format. It's simply surround processing.
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If you don't apply PLIIx to a 6.1 signal, then the mono surround-back channel is simply sent to both rear speakers. That information will image behind you.


If you apply PLIIx to a 6.1 signal, then the processing ignores the discrete surround-back channel. But that's OK, since all the surround-back information is duplicated in the left & right surround channels (this is done for backwards compatibility). So PLIIx will extract sounds for the appropriate speakers. Any sounds meant to image behind you will still be sent to both rear speakers.


The difference is with normal 6.1 decoding, the 2 rear speakers are always run as dual-mono. With PLIIx processing, the 2 rear speakers are run as stereo. That doesn't prevent them from sometimes having the same sound for imaging directly behind the listener.


Sanjay

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But this is ONLY with PLIIx applied, correct? How big of a difference is there between digital and analog audio formats? So anything Dolby/DTS that I send to my receiver (Onkyo TX-SR503) will be digital, w/ or w/out PLIIx? I read somewhere that Pro Logic was a analog format. Not sure if it was PLI, PLIx, PLII, PLIIx, or the difference between those 4. I was thinking that PLI and PLII are surround sound formats, and PLIx and PLIIx were surround sound processing.

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Dolby Pro Logic (the original) was a method of "encoding" 4 audio channels (L, C, R, Surround) into two recording channels (L, R), most notably on analog tape. Dolby Pro Logic refers to both the encoding of that, and the decoding. DPL is a surround format, or, perhaps technically Dolby Surround is a surround format, and Dolby Pro Logic is the decoding scheme for that format (I'm not 100% on what the distinction between Dolby Surround and DPL is, or if there is a distinction).

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There are (to my knowledge) only 3:

Dolby Pro Logic (the original surround encoding scheme)

Dolby Pro Logic II

Dolby Pro Logic IIx


Dolby Pro Logic II is an algorithm to extract 5 channels (L, C, R, SL, SR) from two channels ( L, R ). It is not a format, but a processing scheme, and it happens in a DSP, ie, in the digital domain. It can be applied to digital or analog sources.


Dolby Pro Logic IIx extends DPL II to 7 channels, adding the Surround Back Left and Right output channels. It to, is not a format, but a processing scheme, again happenning in the digital domain.


The big difference between DPL II and DPL IIx, is the additional 2 surround back channels, and that DPL IIx can be applied to 5.1 DD and DTS, to "steer" the SL/SL surround channels in the DD/DTS source around the 4 surround channels. If applied to a 5.1 DD/DTS source, DPL IIx leaves the front stage (L,C,R) untouched.

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DPL is a format, DPL II and DPL IIx are surround sound processing schemes, with "x" being the 7.1 channel version of DPL II.

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I don't think DPLII is a processing scheme. Take a look at this quote [refers to Xbox 360]:


"Analog output

If you use analog Xbox 360 audio output, you can choose between two types of output:


Mono (single-speaker sound)

Dolby Pro Logic II, which works with most analog sound systems:

• Standard stereo TV sound systems


• Two-speaker stereo sound systems


• Simulatedsurround sound systems (such as Dolby Virtual Surround and SRS TruSurround)


• Dolby Pro Logic surround sound


• Dolby Pro Logic II 5.1 surround sound


• ".1"surround sound systems, like Dolby Pro Logic II, can use a subwoofer."

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If you don't apply PLIIx, then the 2 surround channels will simply be sent to 2 surround speakers. I'm not sure if that answers your question or not.
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Since it's your receiver, the answer is a button push away. Don't be afraid, you won't damage anything.
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Not everyone has a 7.1-speaker set-up. Most surround layouts are still 5.1.
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Pro Logic is a matrix decoder, designed specifically to be used on Dolby Surround encoded material. Pro Logic has been implemented as an analogue circuit as well as in the digital domain. Does the same thing in either case.


That would be like me saying that I read somewhere that still pictures are photo-chemical. While that's true, there are also digital pictures. Both do the same thing: capture an image.
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People use the word "format" to mean all sorts of things, which ends up confusing me. So I tend to refer to these technologies as "decoding" or "processing". Of course, the difference between the two depends on whether you're using it on encoded material or not.


If you apply Pro Logic to Dolby Surround material, then it's acting as a decoder. If you apply Pro Logic to a regular CD, then it's acting as a surround processor (there's nothing encoded on the CD to decode). If you apply PLII to a matrix encoded TV show, then you're using it for decoding. If you use PLII with ordinary stereo material, then your using it as surround processing.


Sanjay

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If you don't apply PLIIx, then the 2 surround channels will simply be sent to 2 surround speakers. I'm not sure if that answers your question or not.
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Since it's your receiver, the answer is a button push away. Don't be afraid, you won't damage anything.
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I'm not sure who you mean by "they". But not everyone has a 7.1-speaker set-up. Most surround layouts are still 5.1.
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Pro Logic is a matrix decoder, designed specifically to be used on Dolby Surround encoded material. Pro Logic has been implemented as an analogue circuit as well as in the digital domain. Does the same thing in either case.


It's like me saying that I read somewhere that still pictures are photo-chemical. While that's true, there are also digital pictures. Both do the same thing: capture an image.
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People use the word "format" to mean all sorts of things, which ends up confusing me. So I tend to refer to these technologies as "decoding" or "processing". Of course, the difference between the two depends on whether you're using it on encoded material or not.


If you apply Pro Logic to Dolby Surround material, then it's acting as a decoder. If you apply Pro Logic to a regular CD, then it's acting as a surround processor (there's nothing encoded on the CD to decode). If you apply PLII to a matrix encoded TV show, then you're using it for decoding. If you use PLII with ordinary stereo material, then your using it as surround processing.


Sanjay