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Discussion Starter · #1 ·
are there any receivers and any formats and any content that are truly 7.1, namely where SBL and SBR are distinct from source to speaker? if the answer is "no," do any existing receivers ability to decode dolby 5.1/EX, for instance, mean they can decode any dolby 7.1 were it to show up in the pipe?
 

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There are no discrete 7.1-channel sources. However, there are 6.1 sources, with distinct content on each of the three surround channels: surround-left, surround-right, surround-back.


7.1 surround processing such as PLIIx and LOGIC7 can extract up to 4 unique/distinct surround channels when applied to 2-channel and 5.1-channel sources.


Sanjay
 

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Discussion Starter · #3 ·
sanjay-


according to my AVR's manual, if PLIIX is applied to a dolby EX source it only "extracts" a single 6th channel. is this correct?
 

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EX decoding extracts a single surround-back channel, which is sent to both rear speakers.


PLIIx processing extracts stereo surround-back channels, and you can actually hear sounds move from one rear speaker to the other.


Sanjay
 

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Well, the current audio formats on DVD aren't 7.1 discrete. AAC and Ogg Vorbis are examples of formats that can be. AAC can do 48 channels and Vorbis can do 255.
 

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Discussion Starter · #6 ·
Quote:
Originally Posted by sdurani
EX decoding extracts a single surround-back channel, which is sent to both rear speakers.


PLIIx processing extracts stereo surround-back channels, and you can actually hear sounds move from one rear speaker to the other.


Sanjay
interesting- are you saying PLIIX extracts discrete information, or does it construct it? does the source tell it what to do (is information encapsulated in the bitstream) or does it use an algorithm to do something? i always thought it was merelly a colorizer.
 

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Quote:
Originally Posted by cjv123
are you saying PLIIX extracts discrete information, or does it construct it?
I'm not sure what you mean by "discrete information". The term 'discrete' is usually used to refer to the number of separate channels in the source material. For example: a Dolby Surround encoded source has 4 matrix channels (left, centre, right, surround) but is delivered as 2 discrete channels (for backwards compatibility with stereo systems). Pro Logic decoding recovers the original 4 channels, but that doesn't suddenly make those channels 'discrete'.


Surround processing cannot create additional discrete channels. What it can do is steer particular information from source channels to additional playback channels. Let's go back to the Dolby Surround example. If you play back the 2-channel soundtrack over 2 speakers, you'll hear a normal stereo spread with the dialogue phantom imaging right in the middle of the front soundstage. Of course you have be sitting exactly between the front L/R speakers to hear the dialogue properly located. Listeners located off-axis will hear the dialogue in the speaker they are closest to.


When you activate the Pro Logic circuit, it will extract correlated (in-phase) mono info from the front channels and send it to the centre channel output. This information is actively cancelled from the front L/R channels so that the dialogue is not heard from all 3 speakers. Since the dialogue is now coming from an actual speaker and is no longer a phantom image, it will be heard from the middle of the soundstage; even by listeners located off-axis.


So even though a matrix derived centre channel contains unique information compared to the front L/R channels, it is not 'discrete' as we normally use that word.
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does the source tell it what to do (is information encapsulated in the bitstream) or does it use an algorithm to do something?
Both. PLIIx uses matrix extraction and logic steering algorithms to derive additional channels. But if the source material has matrix encoding, then the result of the processing can often be better because sounds were intentionally placed to be extracted. So even for EX encoded sources, Dolby recommends using PLIIx processing instead of EX decoding during playback.
Quote:
i always thought it was merelly a colorizer.
Again, not sure what you mean by "colorizer". PLIIx doesn't add any sounds or reverb/echo effects during playback. Everything you hear is from the original recording. The main difference is that certain sounds were re-directed based on where they image.


Let's go back one last time to the previously mentioned Dolby Surround example; except this time, think about in the rear hemisphere instead of in front of you. Stereo content in the surround channels will image to your left or right side, but correlated mono info will tend to phantom image behind you. You hear the same sound in both ears and your brain tells you that it is coming from around the centre line. Of course, you have to be sitting exactly between the 2 surround speakers to hear this effect properly. If you are sitting off-axis, those same sounds will collapse to the nearest surround speaker.


When you engage the EX decoding circuit, it extracts correlated mono info and sends it to an additional pair of surround speakers behind you. These sounds are also actively cancelled from the side speakers (so they're not heard from both directions). Now, no matter where you are sitting, those sounds will always image from behind you. Same directionality, but better imaging stability. Just like with the extracted dialogue in the front soundstage.


With 5.1-channel sources, PLIIx processing does basically the same thing as EX decoding, but the rear channels are in stereo rather than dual-mono. Since the surround channels are matrix derived during playback, they cannot be considered "discrete", even though each surround channel will contain different information. I don't know what would be the best word to use: maybe 4 "unique" channels or 4 "distinct" channels?


Sanjay
 

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Discussion Starter · #8 ·
ok, i think i'm close to understanding this.


are you saying PLIIX is capable of decoding (from what i recognize is a 2-channel stream but one which contains a matrix of information- multiplexing if you will- for more channels) 7 distinct encoded channels? if i was a musician and i wanted a series of identical-in-frequency tones to play in a specific contrived pattern SBL, SBR, could i encode my music to play that way? can i record in the SBL knowing it will be decoded to play there?
 

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Quote:
Originally Posted by cjv123
are you saying PLIIX is capable of decoding (from what i recognize is a 2-channel stream but one which contains a matrix of information- multiplexing if you will- for more channels) 7 distinct encoded channels?
PLIIx will output up to 7 distinct channels of information from 2-channel sources, whether they are matrix encoded or not. Meaning if you played a regular 2-channel CD using PLIIx, you would get 7 unique outputs. Since most CDs aren't specifically encoded for surround sound, results can vary wildly.


If you have the DVD of 'Blade II', take a listen to chapter 16. The disc has 2-channel, 5.1-channel and 6.1-channel soundtracks. If you play the 2-channel track with PLIIx, you'll notice that sounds have the same directionality as the discrete multi-channel tracks; you'll clearly hear distinct left vs right vs rear imaging in the surround field.


Keep in mind that the 5.1/6.1 mixes will almost always sound better than the 2-channel downmix. I mean, once you scramble an egg (mix the channels) you can never get it perfectly unscrambled. Still, the 'Blade II' soundtrack is a good example of recovering encoded channels during playback (since it originated from a multi-channel soundtrack), not to mention a very impressive demo of what is possible with only 2 discrete channels.
Quote:
if i was a musician and i wanted a series of identical-in-frequency tones to play in a specific contrived pattern SBL, SBR, could i encode my music to play that way?
Probably. It depends on how good the matrix encode/decode system is that you're using. There is a test CD available from the Boston Audio Society that has a surround sound pan which circles the room. With PLIIx or LOGIC7 processing you can actually hear the sound go all the way around the room, moving from one individual speaker to the next. So even with matrix encoded channels, you should be able to move content between the two rear channels.
Quote:
can i record in the SBL knowing it will be decoded to play there?
If you can figure out what combination of phase/level conditions cause the decoder to steer a particular sound to the SBL channel, then you could encode your content that way. On EX soundtracks, the surround-back channel is encoded as correlated mono info. Upon decoding, those sounds always end up in the rear speakers. If you similarly encode content for the SBL channel, it should trigger the decoder to consistently send those sounds to the left rear speaker.


Sanjay
 
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