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Discussion Starter · #1 ·
So I did a deep dive on matrixed surround sound. I'm still uncertain on a few issues but here is what I gathered:


1. Matrixed sound is more sophisticated than I initially thought. Dolby Pro Logic II (IIx, and IIz and DTS Neo6 and Neo6-ES) extract surround information previously encoded into 2.0, 5.1, and 7.1 recordings (I was not aware that matrixing involed encoding before). The encoding part is apparently reffered to as "Dolby Surround" whereas the decoding part is "Pro Logic." PLII can also extract surround information from unencoded stereo sources by comparing the differences in channel information. I'm guessing that encoded tracks will decode more accurately than unencoded tracks.. So is there a way to identify encoded content in movies and music?


2. The PLII (and IIx) "Music" settings have additional controls to fine tune the sound stage over its Movie counterpart. In the settings on my Onkyo TX SR706 I was able to bring the soundstage forward (solving the bass attenuation of hollow, recessed sounding vocals I was hearing before) and I was able to control the width of the soundstage (preventing to much from being thrust to the surrounds) and the ability to widen the center channel audio. I've got it sounding better now, with a solid bass, full midrange and mostly subtle use of the surrounds for ambience without spreading things too wide. These tweaks make PLII handling of stereo music much better to my ears.


So now some electronic music sounds great with these settings (Booka Shade). However, some 2 channel music still throws it off. Several Led Zeppelin songs that have a kind of chorused effect on the vocals get moved almost completely to the surrounds. Actually, anything with a chorused effect seems to be thrown all the way out to the surrounds. I'm guessing this would not occur if the music was encoded with Dolby Surround
 

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Quote:
Originally Posted by minimalist1969 /forum/post/19626146


So I did a deep dive on matrixed surround sound. I'm still uncertain on a few issues but here is what I gathered:


1. Matrixed sound is more sophisticated than I initially thought. Dolby Pro Logic II (IIx, and IIz and DTS Neo6 and Neo6-ES) extract surround information previously encoded into 2.0, 5.1, and 7.1 recordings (I was not aware that matrixing involed encoding before). The encoding part is apparently reffered to as "Dolby Surround" whereas the decoding part is "Pro Logic." PLII can also extract surround information from unencoded stereo sources by comparing the differences in channel information. I'm guessing that encoded tracks will decode more accurately than unencoded tracks.. So is there a way to identify encoded content in movies and music?


2. The PLII (and IIx) "Music" settings have additional controls to fine tune the sound stage over its Movie counterpart. In the settings on my Onkyo TX SR706 I was able to bring the soundstage forward (solving the bass attenuation of hollow, recessed sounding vocals I was hearing before) and I was able to control the width of the soundstage (preventing to much from being thrust to the surrounds) and the ability to widen the center channel audio. I've got it sounding better now, with a solid bass, full midrange and mostly subtle use of the surrounds for ambience without spreading things too wide. These tweaks make PLII handling of stereo music much better to my ears.


So now some electronic music sounds great with these settings (Booka Shade). However, some 2 channel music still throws it off. Several Led Zeppelin songs that have a kind of chorused effect on the vocals get moved almost completely to the surrounds. Actually, anything with a chorused effect seems to be thrown all the way out to the surrounds. I'm guessing this would not occur if the music was encoded with Dolby Surround

You are a bit confused here. There are two types of playback, one is decoding encoded surround material. The other is adding effect on playback to unencoded materials to simulate surround sound. You cannot as you say extract surround information that isn't there in the first place.


The outcome of surround simulation will be hit or miss because there is no sound in the mix meant to go to the rear speakers. The effects you use upon playback make some guesses based on stereo separation, volume and phase as to which sounds to throw to the rear. Most just give you some reverberant, low level facsimile of the front signal which can give some sense of room ambience. You wouldn't want much more than that else you'll get big errors like vocals coming out the rear.


It is my personal opinion that all recordings should be played back in the format in which they were recorded. Adding effects is seldom an improvement.
 

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Discussion Starter · #3 ·
And I too am often a purist when it comes to stereo playback. My initial experiences with PLII and Neo6 on stereo content was pretty horrible.


But I have to admit, now that I have tweaked my PLII Music settings to compensate for the weird effects was previously experiencing (hollow, recessed sounding vocals, weak bass, content being thrown too far into the surrounds), I can see that some music does actually benefit from subtle PLII processing. I guess the takeaway is that for unencoded 2.0 content, the results really depend on the recording. Some do great and some do some really strange things.


I just dug through some older late 90's DVD's in my collection and came across "Dolby Digital: Stereo Surround 2.0" labels on them. I assume these are encoded to take better advantage of PLII?
 

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Quote:
Originally Posted by minimalist1969 /forum/post/19626146


So is there a way to identify encoded content in movies and music?

Not unless there is a label on the packaging or disc. However, almost all 2-channel music is not matrix encoded whereas almost all 2.0 movie/TV soundtracks are surround encoded. It's extremely rare to find a soundtrack that was mixed to plain stereo, like most music is.
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These tweaks make PLII handling of stereo music much better to my ears.

You're already off to a good start. For 2-speaker listeners trying out PLII for the first time, I typically suggest setting the Centre Width parameter to its widest setting (put your ear against the centre speaker to make sure there is no sound coming from it), and set the Dimension parameter to the front-most setting (as little surround extraction as possible). Set the Panorama parameter to Off.


This should result in a slightly wider than normal soundstage with a phantom centre image that you're used to. From this base-line, you can start experimenting to find out how much centre and surround extraction sounds good to you. Don't hesitate to vary the settings from recording to recording, genre to genre. Pop music can sometimes sound more fun and exciting with agressive settings that would normally be distracting with chamber music. You won't hurt anything by trying and you can always tame down the processing.
Quote:
just dug through some older late 90's DVD's in my collection and came across "Dolby Digital: Stereo Surround 2.0" labels on them. I assume these are encoded to take better advantage of PLII?

"Dolby Digital" is the lossy compression codec used, "Surround 2.0" means matrix encoded.
 

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Discussion Starter · #5 ·
The settings I used were the precise ones you suggested. I did turn the Panorama setting back on and found that with the soundstage set to the front most setting its effect was quite subtle. When the soundstage gets moved further back the Panoramic setting seems more extreme.


So what I think I hear you saying is that any DVD with a Dolby symbol is likely matrix encoded, on top of any 2.0, 5.1, or 7.1 discrete encoding that is also present?


When I put an older Dolby Digital: Stereo Surround disc into my blu-ray player (bitstreaming via HDMI to my Onkyo AVR) I notice that Stereo mode is not available when I cycle through the movie listening modes (yet it is available when I cycle through the Music listening modes). Does this imply that the receiver thinks the default setting should be PLII?
 

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Quote:
Originally Posted by minimalist1969 /forum/post/19626810


I did turn the Panorama setting back on and found that with the soundstage set to the front most setting its effect was quite subtle. When the soundstage gets moved further back the Panoramic setting seems more extreme.

Quick explanation of what Panorama does:


After PLII sends, for example, dialogue to the centre speaker, that centre signal then is sent back to the L/R channels out of phase. This extra step causes that information (dialogue) to be cancelled from the L/R speakers (leaving everything else intact). Otherwise, you'd hear dialogue out of all 3 front speakers. And that would sound bad.


Likewise, when surround information is extracted, some front L/R information invariably leaks to the surround speakers. So, the front L/R info is inverted and sent as a cancellation signal to the surround speakers. This keeps that information in the front soundstage. Otherwise, having some of that info in the surrounds would cause the front soundstage to spread really wide and give a wrap-around effect. And that would be bad.


Or would it?


Turns out for some sources (studio pop/rock), it can sound really nice. Maybe not realistic, but pasted together studio pop music has hardly any basis in reality anyway. On the right type of music, the larger-than-life effect can be lots of fun. So PLII allows you to choose whether front leakage is cancelled from the surrounds or not. Want to hear a large, panoramic soundstage? Set the Panorama parameter to On (no cancellation signal sent). Want it more realistic? Turn the Panorama setting Off (front info cancelled from surrounds).


Your ears will decide when it sounds good and when it doesn't. But at least you know what it's doing.
Quote:
So what I think I hear you saying is that any DVD with a Dolby symbol is likely matrix encoded, on top of any 2.0, 5.1, or 7.1 discrete encoding that is also present?

Dolby licenses a lot of products: lossy compression (DD, DD+), lossless packing (MLP, TrueHD), matrix encoding/decoding (Surround EX, Dolby Surround, Pro Logic), Surround processing (PLII, PLIIx, PLIIz), etc.


So seeing the Dolby symbol on a DVD can mean any number of things. In the case of most DVDs, it usually represents the use of lossy compression (DD). If the DVD soundtrack is 2-channel, then the Dolby symbol likely also means that it was matrix encoded using Dolby Surround. 5.1 EX soundtracks are also matrix encoded using Surround EX (surround-back channel folded into the L/R surround channels).
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When I put an older Dolby Digital: Stereo Surround disc into my blu-ray player (bitstreaming via HDMI to my Onkyo AVR) I notice that Stereo mode is not available when I cycle through the movie listening modes (yet it is available when I cycle through the Music listening modes). Does this imply that the receiver thinks the default setting should be PLII?

Yes. Sounds like the manufacturer assumed that you'd never want to listen to a 2.0 movie soundtrack using 2 speakers, so they left Stereo out of the menu for the movie modes. Just a choice in functionality, not a limitation of the processing.
 

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Discussion Starter · #7 ·
It seems that the difference between discrete and matrix surround technologies is not so cut and dry and that often they are used in conjunction with one another during the encoding process.


If I understand correctly, discreet Dolby Digital comes in 3 flavors (1.0, 2.0, and 5.1) and Pro Logic is used to decode the extra channels that were matrix encoded on top of the 6 discreet channels. Hence, George Lucas encodes Star Wars as DD 5.1 EX and the "EX" only gets activated if your receiver has Pro-Logic IIx and you have the extra surrounds connected.


What happens if you listen to a 7.1 TrueHD or DTS-HD MA track and you only have a 5.1 setup? Are Pro Logic IIx or Neo6-ES being used to down-mix those tracks?
 

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Quote:
Originally Posted by minimalist1969 /forum/post/19627699


Hence, George Lucas encodes Star Wars as DD 5.1 EX and the "EX" only gets activated if your receiver has Pro-Logic IIx and you have the extra surrounds connected.

EX can also play on its own. My old 7.1 setup had the option of playing EX encoded discs without activating ProLogicIIx, but EX sends a mono signal to the rears for 6.1, so I always kicked on PLIIx anyway to get 7.1. Not sure of the exact process.


Same thing with DTS-ES Discrete discs. I could also run those on my system without ProLogicIIx, but usually turned on the matrixing anyway to get full use out of the rear surrounds.

Quote:
What happens if you listen to a 7.1 TrueHD or DTS-HD MA track and you only have a 5.1 setup? Are Pro Logic IIx or Neo6-ES being used to down-mix those tracks?

They play as TrueHD or DTS-HD and the rear surrounds get mixed in with the side surrounds, as if it were a 5.1 track to begin with.
 

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Quote:
Originally Posted by minimalist1969 /forum/post/19627699


What happens if you listen to a 7.1 TrueHD or DTS-HD MA track and you only have a 5.1 setup? Are Pro Logic IIx or Neo6-ES being used to down-mix those tracks?
Quote:
Originally Posted by Tulpa /forum/post/19627793


They play as TrueHD or DTS-HD and the rear surrounds get mixed in with the side surrounds, as if it were a 5.1 track to begin with.

It would be more correct to say that the BD soundtrack authoring process includes the instructions about how to produce 2.0, 5.1, and 7.1 mixes from the individual TrueHD or DTS-HDMA disk; the specifics are not discretionary to the decoder. (But in the case of a multchannel LPCM soundtrack, it all seems to be up to the decoder 'to do whatever it wants'.)
 

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I felt mine was correct enough.
Guess not.
 

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Discussion Starter · #11 ·

Quote:
Originally Posted by SoundChex /forum/post/0



It would be more correct to say that the BD soundtrack authoring process includes the instructions about how to produce 2.0, 5.1, and 7.1 mixes from the individual TrueHD or DTS-HDMA disk; the specifics are not discretionary to the decoder. (But in the case of a multchannel LPCM soundtrack, it all seems to be up to the decoder 'to do whatever it wants'.)

I wonder if this could explain why so many people in my family (mostly older people mind you) have such a hard time understanding dialog on DVDs played through their internal tv speakers (yet they have no trouble with broadcast tv or cable channels). Could it be a down mixing issue? In our own household we noticed movie dialog got a lot easier to understand with a proper 5.1 system and a good center channel. Even when there are explosions all around the dialog comes through crystal clear.
 

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subscribed... good thread... nice explanations by sanjay...



and kudos to you minimalist...
 

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Quote:
Originally Posted by Tulpa /forum/post/19627872


I felt mine was correct enough.
Guess not.
As you can see from the DTS-HDMA downmix control panel shown: The (presumably default) setting for a 7.1 Standard to 5.1 Standard downmix is to roll the Rear Surround content into the corresponding (Side) Surround channels. However the panel provides for the Channel 7/8 content to be redistributed elsewhere--or even discarded--at the sound mixer's discretion, and for level rebalancing the resultant 5.1 downmix (e.g., to affect the overall soundtrack presence...?)


[And we would of course expect the downmix configuration setting to be correspondingly more complex when the original soundtrack is something other than 7.1 (6.1) Standard . . . and Channels 7/8 not simply Left and Right Rear Surrounds.
]


 

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*head explodes*
 

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Quote:
Originally Posted by minimalist1969 /forum/post/19627699


It seems that the difference between discrete and matrix surround technologies is not so cut and dry and that often they are used in conjunction with one another during the encoding process.

Yes. And that's because the number of channels in the source material doesn't always match the number of speakers used for playback. Dolby Surround material is 4 matrixed channels (L,C,R,S), delivered as 2 discrete channels, played back over 5 speakers. Notice that none of those numbers match.


It may be less complicated to think of surround processing the way we think of video scaling. People have no problems scaling 480i and 1080p material to their 720 display. But when it comes to audio, 2-channel has to be played back over 2 speakers, 5.1 channels over 5.1 speakers, etc. This is the equivalent of watching a standard def DVD using only a 480x720 grid of pixes in the middle of your high def display. Nobody does that. We scale all sources to the number of pixels in the display. And no one complains that the video processor is making up video content that was never there.


To that end, I've been running a 7.1-speaker layout since the early 1990s. All audio sources get scaled to my set-up, irrespective of the number of channels. Just like with my video display. The surround processing isn't perfect, just as the video scaling isn't perfect. But the vast majority of the time it works fine.
Quote:
If I understand correctly, discreet Dolby Digital comes in 3 flavors (1.0, 2.0, and 5.1) and Pro Logic is used to decode the extra channels that were matrix encoded on top of the 6 discreet channels. Hence, George Lucas encodes Star Wars as DD 5.1 EX and the "EX" only gets activated if your receiver has Pro-Logic IIx and you have the extra surrounds connected.

DD is a lossy compression algorithm, like MP3 or AAC. As such, it can be any number of channels, from 1.0 to 5.1 (and any variation in between). There are a couple of DD 4.0 quad mixes floating around.


George Lucas's sound designer, Gary Rydstrom, got together with Dolby and THX to devise a way to encode a third surround channel (the surround-back channel) in a way that was backwards compatible with 5.1 systems. They split the surround-back channel equally between the surround-left and surround-right channels (EX encoding). When played back on a 5.1-speaker layout, the surround-back info would phantom image exactly in between the 2 surround speakers, appearing to come from behind you. When played back on a 7.1 set-up, EX decoding would extract the surround-back info, send it to the rear speakers and cancel it from the side speakers. The EX decoder is like the front part of a Pro Logic decoder: i.e., takes 2 channels and extracts a centre output. Apply it to the 2 surround channels and the centre output is the surround-back channel. Simple encode/decode.
Quote:
What happens if you listen to a 7.1 TrueHD or DTS-HD MA track and you only have a 5.1 setup?

TrueHD has kind of nested structure: inside the 7.1 mix is a 5.1 mix, inside the 5.1 mix is a 2.0 mix. For a 5.1-speaker layout, the 5.1-channel stream is played back (contains all the information of the 7.1 mix, just in fewer channels). So there's no need to downmix. By comparison, I *think* DTS-HD MA decodes the full 7.1 track and downmixes to 5.1. Different approaches, same result.
Quote:
Are Pro Logic IIx or Neo6-ES being used to down-mix those tracks?

No need to. The downmixing is done in such a way that it is compatible with PLIIx, EX and ES decoding. Suppose I mix a CD with the lead vocals split equally between the L/R channels. You apply PLII during playback, and it extracts anything that is the same in both channels, and steers it to the centre (where it would have phantom imaged anyway). Notice I didn't have to use PLII encoding for it to decode properly with PLII later on. The same can be done with downmixing 3 or 4 surround channels to 2.
 

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Discussion Starter · #16 ·
So it seems as if all the latest and greatest surround technologies for DTS and Dolby are aware of all the other technologies from within their own companies. It is cool that the DTS and Dolby encoders give the sound designer the ability to control how the mix will sound on each setup as you move down the food chain.


Any ideas on why so many people seem to have problems hearing dialog on DVD's and Blu-ray played on 2 channel TV speakers? I have tried to help several family members with this problem. One got an inexpensive Vizio soundbar/subwoofer combo (not 5.1, just SRS surround) and although the fidelity is better I could never make the vocals stand out because there are no controls for a center channel). I assumed it was due to movies being mixed for 5.1 but now I'm not so sure. Could it be a down-mixing issue?
 

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Quote:
Originally Posted by minimalist1969 /forum/post/19628689


So it seems as if all the latest and greatest surround technologies for DTS and Dolby are aware of all the other technologies from within their own companies.

Yes, the industry has done a pretty good job with cross compatibility (and backwards compatibility).
Quote:
It is cool that the DTS and Dolby encoders give the sound designer the ability to control how the mix will sound on each setup as you move down the food chain.

Agreed. Even better is that they gave you the ability to control how the surround processing will sound on your set-up. Being able to decide just how much centre and surround information you want to extract can make the difference between an enjoyable enhancement versus an annoying distraction. I hope you keep experimenting with tailoring the PLII adjustments to your tastes.
Quote:
One got an inexpensive Vizio soundbar/subwoofer combo (not 5.1, just SRS surround) and although the fidelity is better I could never make the vocals stand out because there are no controls for a center channel).

Related discussion here: http://www.avsforum.com/avs-vb/showt...=#post19623091
 

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According to Dolby , matrix encoding 'additional channel' content offers even more possibilities:
Quote:
"Movie and game producers can even mix specific height channels into a soundtrack, and Dolby Pro Logic IIz will faithfully reproduce the vertical placement of those sounds."

[This Home Entertainment Magazine article briefly discusses a DPLIIz encoded game.]


So perhaps someday we might see a TrueHD BD with an alternate DDPlus soundtrack nominally 5.1/7.1 Standard speaker configuration, but specifically encoded with ('near discrete') DPLIIz height channel content...?!
 

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Discussion Starter · #20 ·
I wonder why Dolby doesn't just make all their formats discreet with built in down-mixing and up-mixing instructions? I guess that might create problems for people without the latest AV receiver processing so instead we get a patchwork mix of discreet and matrixed standards. And I guess we have to keep in mind that each of these standards was created at a speciifc time with specific technical limitations.
 
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