Surround Sound Setup THX vs Dolby 7.1/7.2

If you read the rest of the THX article, their layout agrees almost 100% with Dolby for TrueHD placement (it also deals with dts-HD). It also has suggested/required settings for your THX A/V receiver (related to THX-ASA, which the article also explains). The reason the first layout looks like it does is because its designed to support THX ASA, as the article explained, see here:
http://www.thx.com/consumer/thx-tech...d-sound-modes/

That, combined with the fact that there really isn't much 6.1/7.1 content available, and 7.1 wasn't really possible (as discrete channels) until Blu-ray/HD-DVD; re-creating that 6.1-esque layout makes sense from a channel mapping perspective. So the THX ASA configuration is designed to enhance that 5.1 layout, much like Harman's LOGIC7 and Yamaha's CinemaDSP - it's a feature on THX receivers.


DTS always draws the prettiest pictures, basically this is what Dolby and DTS want you to do for TrueHD/dts-HD though:


So the real question is, do you have a THX receiver?

The THX recommendations for surround-back speaker placement make no sense. Lossy soundtracks and their lossless counterparts differ in fidelity, not surround content. Yet THX would have go from surround-back speakers almost touching to spreading them 60 degrees apart just because you switch from a legacy codec to one of the newer lossless codes (TrueHD, DTS-HD MA).

Yeah, I've never heard anything magical about TrueHD or DTS-MA that requires different speaker layouts than their lossy counterparts.

It would be helpful if we could find some (credible) study of 7.1 layout listening environment "quality" in which the only variable was rear speaker separation.

Apropos this question: The Owner's Manual 7.1 channel speaker layout setup instructions for the Yamaha RX-V667 (with TrueHD and DTS-HDMA, but not THX) require only that the rear speaker pair be separated by "12 inches or more":

You're looking at the wrong element - as THX explained in the ASA article, the combined 7.1 placement deals with the fact that you're taking 5.1 content in. It has nothing to do with "fidelity" - 7.1 doesn't exist for Dolby Digital or DTS, period. You can get matrix 6.1 from DD-EX and DTS-ES, and those rare DTS-ES Discrete 6.1 tracks - thats going to map 1:1 through their ASA suggestion. The reason they further suggest this, again if you'd read, is because this array supports ASA 7.1, which is a resampling method - not a discrete surround format.

If you'll notice, none of the THX, Dolby, or DTS layouts differ in their 5.1 layouts - which is where your actual content is coming from, everything else is coming from matrix/synthesis; except for those newer codecs (like dts-HD) which can support 7.1 as discrete content, which assumes those rear surrounds can be treated as independent in-line with their placement.

Fidelity has nothing to do with this, actual content does. And there can be a difference in actual content between these codecs, again, as the "legacy" codecs do not support 7.1, the newer stuff does.

When scaling legacy soundtracks to a 7.1-speaker layout, the number of discrete input channels doesn't matter. Are the 2 discrete channels of a Dolby Surround encoded DVD or TV show "going to map 1:1" to a THX 7.1-speaker layout? I think not.

So all legacy sources will have to be scaled, irrespective of the number of discrete channels. In which case, why would anyone be using EX or ES decoding to get 6.1 outputs when they could be using PLIIx or Neural processing to get 7.1 outputs, especially for a 7-speaker layout?

With the surround-back channels being stereo, not dual-mono, it doesn't make sense to place the rear speakers right next to each other. You'll never hear the stereo separation, especially behind you, where our human hearing is not that great.

BTW, when Surround EX first came out, THX recommeded the rear speakers be spread apart for 7.1 layouts. Placing the rear speakers together didn't show up until their Ultra2 spec later on. Arbitrary, but thankfully being corrected (albeit with lossless codecs as an excuse).
Same content, delivered in fewer discrete channels. Don't take my word for it: compare a discrete 7.1 soundtrack to its 5.1 companion/core via PLIIx, and you'll hear content from each of the 4 surround speakers track the same between the discrete and matrixed presentations. This wouldn't be possible if there was a "difference in actual content".

It's makes no sense for THX to recommend spreading the rear speakers apart only for Dolby TrueHD and DTS-HD Master Audio, since they can be any number of channels. If the recommedation was meant for 7.1 discrete, then say so, rather than using codecs. After all, DD+ and DTS-HD HR and PCM are all capable of delivering 7.1 discrete channels. And it doesn't even make sense to limit it to discrete, since surround processing can yield 7.1 independent channels (stereo sides and stereo rears).

The original point I was trying to make is that this configuration can be ignored if your equipment doesn't support it. If you've got a THX receiver that does ASA, that is how THX suggests you to set things up (and if you refuse to read the user's manual, that's your own choice); if you don't, then it can be ignored because it does not apply to your equipment or situation. Hence the question "Do you have a THX receiver?".

This is an entirely moot point if the processor in question is not a THX processor, it won't even recognize ASA modes. Like the Yamaha manual for a non-THX part; the ASA configuration doesn't even enter into the equation (and indeed, I've never seen this 7.1 configuration outside of ASA - it probably does make sense from the perspective of the ASA decoder).

Regarding why they didn't label things as you would've, I really can't answer that - but I'm sure you could e-mail them and ask if you're curious (or perhaps we have some THX techs that can weigh in on this). Can't say I'm not wondering about that too, now.

Looking at THX's documentation further, this (ASA) looks a lot like CinemaDSP at least in terms of its intention - and I know that CinemaDSP does not follow fully conventional layouts either, simply by nature of its processing methodology; the way Yamaha will suggest a Tri-field/Quad-field array to be configured doesn't match any current Dolby or DTS layout for 7.1 or 9.1 (let alone 11.1), despite being "correct" for that equipment.

You've mentioned ASA a dozen times in this thread (six times in the last post alone), likening it to LOGIC7 and CinemaDSP, referring to it alternatively as "modes" and a "configuration" and even a "decoder" (is there ASA encoded material?). Can you tell me what ASA is or what it does?

This has always confused me as well. THX ASA? I have a THX system meaning I have a THX ultra2 receiver and THX certified speakers in a 7.1 configuration. I almost always watch movies with THX processing engaged. Call me a THX fanboi It just sounds good to me.

So the THX website suggests to put your two rear speakers together and engage the ASA circuit. Then on the same page it says if you are watching a Dolby True HD or DTS HD blu ray you are told to seperate the rear surrounds and disable the ASA circuit.

So...according to THX you need to seperate your back speakers if you are watching Megamind in 7.1 but when you then switch on Transformers in 5.1 and use THX ultra2 cinema to matrix the two rears you need to move em back together and engage the ASA circuit?

This makes absolutely no sense

Please, allow me to confuse you further. Remember what you wrote in the previous paragraph: rear speakers apart for Dolby TrueHD and DTS-HD MA. THX never mentions anything regarding the number of channels.

So, if you're listening to the TrueHD 5.1 soundtrack on 'Transformers' using the THX mode, then the two rear speakers need to be apart. But if your player is connected via optical or coax, and you're listening to the DD 5.1 track via the THX mode, then the rears need to be together. Got it? TrueHD = apart. DD = together. Same 5.1 soundtrack. Same THX processing.

THX needs to send me my own personal THX rep to stand in my home theater and move my speakers around each time I switch codecs

ASA stands for "Advanced Speaker Array" - my first post has a link to THX's web-page that explains what it does. It looks a lot like CinemaDSP from the advertising pictures (they have the same "recreate a movie theater in your home" imagery and slogans). My understanding is that ASA, like CinemaDSP or LOGIC7, attempts to recreate a soundfield or surround environment with more speakers than the material has; and that this explains the awkward 7.1 placement (their pictures seem to indicate this). But I've never seen a receiver with ASA, so I'm not certain of this. I doubt if there is material that comes with this branding though (so the use of the word "decoder" was probably wholly inaccurate - whoops ).




THX doesn't say to disable ASA in this configuration, they have the following to say: "If you use Dolby® TrueHD or DTS-HD Master Audio™, your back surround speakers should be separated to produce a 60° angle from the main listening position. In addition, you should go to the “THX Set Up” Menu in your THX Certified AV Receiver/Pre-amp and set the ASA Surround Back Speaker setting to “Apart (greater than 48).”"

My understanding of THX's labeling scheme is thus:

The Ultra/Plus/Select stuff refers to the type/class of receiver you have; not any specific processing modes. Nueral/ASA/EX stuff refers to types of processing features that THX receivers all have in common; but not any specific standards (like Dolby).
This is what I cite as evidence:
THX Certification Performance Levels:
http://www.thx.com/consumer/home-ent...ce-categories/
THX AVR Features:
http://www.thx.com/consumer/thx-tech...iver-features/ (this has a link to the same ASA page as linked earlier)

This could be entirely wrong; as their online information seems to be about as straight-forward as the Iran-Contra affair.

Wait, what?

A 7.1 receiver set up for 5.1 should be sending surround channels to the side surrounds, because in 5.1 the surrounds are side surrounds. 7.1 adds the rear surrounds.

Also, 7.1 content isn't needed for 7.1. ProLogicIIx will matrix the surround channels of 5.1 into all four surround speakers. Works quite well IMO, despite what the naysayers will have you believe.

Most if not all 7.1 receivers will kick in ProLogicIIx for 5.1 content to send it to all four speakers by default. They don't remain silent for 5.1 material, Blu-ray or otherwise, unless you turn off the rear surrounds in the receiver's setup menu; then you'll get the surround info from the side surrounds (5.1 setup of a 7.1 receiver.)

Tulpa is correct, as usual.

5.1 set-ups typically had a single pair of surround along the sides, but slightly rearward of the listening area in order to create some phantom imaging behind the listeners.

As consumer systems went beyond 5.1, surround-back channels were added inbetween the L/R surround channels. Adding a pair of speakers behind you allowed the original surrounds to be moved up a bit, putting them directly to the sides to stabilize lateral imaging.

BTW, I've been running a 7.1-speaker set-up since the early 1990s (a few years before there was any discrete 5.1 material). Doesn't matter if I'm playing a 2-channel CD or a 5.1-channel movie, none of my speakers are silent; and neither should your's (unless you want them to).

OK, it's apparent you can't explain it in your own words because you don't actually know what ASA is. In that case, let's start at the begining.

Ever hear of Hughes SRS or Spatializer? It was the kind of crosstalk cancellation processing that made a pair of speakers sound like they were further apart than they physically were. It was popular for TV sets, giving almost a pseudo-surround effect from the two built-in speakers.

That's basically what ASA is. And that's why, during initial set-up of a THX receiver, you had to dial in how far apart your rear speakers were. The wider apart they were, the less SRS processing they needed. THX wanted you to place the speakers close together only to then apply spatializer-like processing to make them sound like they're further apart. Seriously? Better and simpler solution: spread the speakers apart physically (instead of virtually), like they used before the Ultra2 spec.

ASA is completely different technology than Lexicon's LOGIC7 and Yamaha's CinemaDSP that you were likening it to; not even in the same category. Think of surround processing as coming in two flavours: extracted ambience and generated ambience.

CinemaDSP is an example of the latter, as are the various Hall, Club, Church and Stadium modes you see on some receivers. They generate reverb and early reflections in order to give the impression of a larger listening space. Nothing wrong with that, as long as you understand that they add things (echos, reverb) that weren't in the original recording.

Yamaha even goes the extra step of sampling the impulse response and decay characteristics of real-life venues for some of its DSP modes (hence specific mode names like Roxy Theatre, Village Vanguard, Bottom Line, etc). Sony does the same with some of their theatre modes, which sound remarkably like their screening rooms here in Los Angeles. If room simulation is your preference, then these are the modes for you.

By comparison, LOGIC7, Dolby PLII (IIx, IIz), DTS Neo:6, Neural, Circle Surround, etc, are examples of ambience extraction. They use only the sounds in the recording itself, steering them to various speakers based on intensity and phase. Nothing is added. With 2-channel material, correlated (in-phase) mono sounds go to the centre speaker, which is where those sounds would have phantom imaged anyway. Decorrelated (out-of-phase) info is steered to the surround speakers. With 5.1 material, surround information that would normally have phantom imaged behind you is extracted and steered to the speakers behind you. The remaining surround information is sent to the speakers at your sides.

So, ASA (which is only applied to the rear speakers) is nothing like LOGIC7 which is nothing like CinemaDSP. And it certainly isn't some magic bullet that can compensate for poor speaker placement. Spreading the rear speakers apart makes it easier to hear stereo separation back there, allows for smoother pans around the surround field, improves rear envelopment, minimizes imaging reversals, prevents hot-spotting in the middle of the back wall, etc. Those are amongst the reasons why I think placing the rear speakers together is a bad idea. Like I originally said, it is one THX recommendation that doesn't make sense.

I do believe ASA was developed by THX with the advent of 6.1 systems. The idea was to effectively decorrelate the two speakers (with mono rear surrounds) to provide a diffuse environment for movie tracks yet provide more a point source for 6.1 music tracks. It was also intended for 7.1 steering systems providing dual mono rear surrounds.

You will not find ASA listed in the list of THX "stuff" on a surround processor, nor will you find their BGC; however, you do have it when you have a set up option to specify the distance between the two rears and an ASA Off selection.

Thanks Sanjay that asnswers a question I was going to ask if I'm watching a blu ray that is 5.1 tru HD or DTS-MA on my 7.1 system should I always have pro logic IIx running to matrix it out to 7.1 or just play it in 5.1 and is pro logic IIx always a better alternative than dts neo 6 even for dts and dts hd-ma content?

I prefer to use 4 surround speakers, for better wrap-around envelopment and greater imaging stability in the surround field. Problem is: how do you spread 2 surround channels to 4 surround speakers?

You can have the rear speakers duplicate the sides, but then you won't get any rear-vs-side separation. You can use Neo:6, but that only extracts a mono surround-back signal (still sent to both rear speakers). If you're going to use 2 rear speakers, might as well send them stereo surround-back signals; which is what PLIIx does.

So I always prefer to have PLIIx running with 5.1 (and 2-channel) sources. All 4 surround speakers get used and each one gets an independent signal (stereo sides, stereo rears).

That makes some sense of their information. Any thumbs up/down on how well it actually does what it says it does?

Sanjay,
I'm very impressed - you went from having no clue what was being discussed to being a field-leading expert. Bravo my good sir! You win the Internet, and may now proceed to the next level.


Tulpa,
Yes and yes. I have seen 6.1/7.1 units that let you run "straight" though, where the rear surround(s) are silent if the source material doesn't have anything for them; but the user usually has to explicitly tell the AVR to do this. ProLogic IIx/z does a fine job with 5.1 -> 7.1; my issue is with 1.0/2.0 -> 6.1/7.1 from a non-matrix track.

You really believe that at any point in this thread I had "no clue what was being discussed"? That's awesome.

Take it with a grain of salt as this guy recommended Bose in a different thread a few days ago.

Thank you very much that is very helpful. I wasn't sure before it the surround and surround backs were duplicated or seperate channels.

Man thats real informative I appreciate that post

some posted earlier that pro logic IIx will extract the two surround back channels almost exactly from a 5.1 source as it would sound if you watched the same movie in a 7.1 format. Can anyone verify that statement. I think thats great if it is.

Movies in 7.1 format are mixed by engineers. So the panning and specific sounds are tested by human ears before committed. The maxtirxing software relies on algorithms and how the sounds pan between two surrounds in a 5.1 soundtrack.

It's not EXACTLY the same, but in the vast majority of movies you're not going to get overly complicated effects back there, so PLIIx will do what the engineer will do most of the time, and the rare times it won't, you probably won't notice, as there is usually a ton of other things going on during the movie.

The only real way to test is to find a movie that has both 5.1 and 7.1 soundtracks, and try it both ways. I doubt anyone has actually done that test.