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Discussion Starter · #1 ·
I read an interview with Dr. Davis Griesinger of Lexicon (the creator of Logic7) and would like to hear your thoughts. He said:


1. "My work suggests that two sub-woofers is better than one"


Do you think this is true in most cases?


2. "There is no question to me that a five channel front sounds

better than a three"


If this is true how would I go about implementing a five channel

front?


3. "Putting two speakers in the ceiling gives you a feeling that

things are more correct"


Do you think this is true?


4. "My ideal speaker configuration is five front, four in the rear, two in

in the ceiling. the five front being left,left center,center, right

center and right.


Do you think this is over-kill?


5. "All these extra channels can be matrix-derived so the only

discrete encode format you would need is 5.1"


What are your thoughts on this?




Curious Chris
 

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I believe the extra front and ceiling speakers to be overkill. But I do agree about extra subwoofers.


I have an MC-12 and use all 3 subwooffers that it supports. Left, Right, and LFE. And 3 are much better than 1.
 

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Well the LFE is in the center of the room under a coffee table. The left sub is at the far left or the primary couch, sort of acting as an end table. And the right sub is on the far right of the big comfy recliner, also acting as an end table. Seems to work.
 

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Discussion Starter · #5 ·
I thought all subs were for low frequency effects. What are you differentiating when you refer to your Left sub, right sub and then your LFE? Sorry if this turns out to be a stupid question-I'm new to this relatively to this.


Chris
 

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The MC-12 provisea a left/right sub. This outputs frequencies below what your main speakers will handle. In other words if you have your left/right speakers set at 60hz, then anything below 60 will go to the left and righ sub respectively.
 

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"In other words if you have your left/right speakers set at 60hz, then anything below 60 will go to the left and righ sub respectively."


That isn't quite correct. If you have your mains at 60hz, all your surrounds + center set at 100hz and the L/R SUB set at 100hz the L/R subs will receive info from 100hz and down.


Shawn
 

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Chris,


"What are you differentiating when you refer to your Left sub, right sub and then your LFE?"


When you use all three sub outputs the Left sub is the left side bass from your main speakers, right is right and the LFE sub is *only* the LFE channel on DD/DTS material.


Why you may want L/R subs has to do with expanding envelopment and spaciousness of the bass though Lexicon's Bass Enhance processing. You can read more info about it from its creator at:

http://world.std.com/~griesngr/sfaes.html


Shawn
 

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Quote:
Originally posted by Chris Bone
I read an interview with Dr. Davis Griesinger of Lexicon (the creator of Logic7) and would like to hear your thoughts. He said:


1. "My work suggests that two sub-woofers is better than one"


Do you think this is true in most cases?
Yes, especially since parallel research by ATT Labs and Dr. Griesinger suggests that some localization cues (such as ITD fluctuations) are operating above 40 Hz, even though traditional thinking says bass below 80 Hz is supposed to be nondirectional. He also makes the point in that interview that if the crossover point is 40 Hz or below, a single sub can be sufficient (provided it can deliver the necessary SPLs, of course).

Quote:


2. "There is no question to me that a five channel front sounds

better than a three"


If this is true how would I go about implementing a five channel

front?
You can't. Dr. Griesinger was speaking theoretically. In order to implement this you would need a surround processor capable of delivering the appropriate signals to this speaker array. The necessary algorithms to do this have never been put into a commercial product.

Quote:


3. "Putting two speakers in the ceiling gives you a feeling that

things are more correct"


Do you think this is true?
Dr. Griesinger was speaking about the results from his psychoacoustic research. Since no commercial audio system is available that utilizes such a configuration, no one here is in a position to say whether it is true or not. Moreover, your quote is incomplete, and misses a key point Dr. Griesinger was making in that interview: such a configuration would only be beneficial in the case of highly absorbant ceilings that remove the spatial realism of height reverberations--with hard reflective ceilings, the speakers would not be necessary. Perhaps it would be more useful to point readers to the actual interview at:
http://www.smr-home-theatre.org/Lexicon/dg_qa1.html

Quote:


4. "My ideal speaker configuration is five front, four in the rear, two in

in the ceiling. the five front being left,left center,center, right

center and right.


Do you think this is over-kill?
Again, you make it sound like this is something you need to worry about implementing. Dr. Grieinger was speaking theoretically, he wasn't recommending it was something you can or should put in your home. Since no commercial system supporting this exists, it isn't an option. However, for anyone who's heard the remarkable experimental 10.2 system Tom Holman has been demonstrating at trade shows and industry events, there's nothing overkill in principle about the use of that many speakers.


Also, taking this quote out of context obscures his clarification elsewhere in the interview that of the four "rear" speakers, two must be positioned directly at the sides (at 90 degrees) for stable side imaging.

Quote:


5. "All these extra channels can be matrix-derived so the only

discrete encode format you would need is 5.1"


What are your thoughts on this?
With this comment, Dr. Griesinger was trying to counter the popular assumption that we need to keep changing the delivery formats to keep adding more discrete channels. He's pointing out that 6 discrete channels (the current standard) are sufficient to support all the information needed for an ideally immersive speaker configuration. However, it would require a surround processor with matrix decoding support for the additional channels. Again, no such processor exists (although the fact that there are two currently unused outputs on the Lexicon MC-12 suggests Dr. Griesinger is working on support for additional channels. At this year's CES, however, he said he hasn't decided what use to make of them at this point).


Cheers,

Philip Brandes
 

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quote:

--------------------------------------------------------------------------------


2. "There is no question to me that a five channel front sounds

better than a three"


If this is true how would I go about implementing a five channel

front?

--------------------------------------------------------------------------------




There was an aritcle published by "Widescreen Review" that discusses this issue in some depth. A relatively simple solution is provided for creating additional matrixed front channels from the existing three channel array, as well as extracting the infrormation for the five front channels from Sony's SDDS format and the Todd-AO format.
 

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"They provide a relatively simple solution for creating additional matrixed front channels from the existing three channel array"


Sure, you could do it the same way the add on decoder boxes can do a rear center channel. In fact using two of them would let you do it.


It would of course have all the same problems as those add on decoder boxes. That being they are not working on a full line level signal... but are instead working on an attenuated signal. This will dramatically decrease the signal to noise ratio of your most important speakers.


Having the matrixing built into the processor, in the MC-12 if Lex. decided to put those 2 extra channels to this purpose, would result in a much higher quality process. Because decoding will be at full level as well as being done digitally (not analog like in those boxes). Would also be much easier to use, setup and adjust.


Shawn
 

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Additionally, you would have to forgo any time alignment on your front three.... otherwise you would be changing phase between them which would screw up the add on boxes decoding. This would mean your front five wouldn't be time aligned. That isn't good. Proper time alignment of the center to the L/Rs is highly audible on music and makes a big difference in the overall sound quality.


For the same reason bass management would need to be the same between center and L/Rs.


If it was internal none of these limitations would apply.


Shawn
 

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Would something like an old Dynaco Quadapter do the trick to create five front channels - or four rears? Not as good as DSP, but "cheap".
 

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The Dynaco box has like 3db of channel seperation. It was intended to try to add ambiance to stereo listening.


In a stereo system you can get the same effect by wiring a surround (or two in series) across the + leads of your stereo amp.


I don't think you could really use one in a surround sound system.... Well of course you could use it but I don't think it would improve anything. ;)


Shawn
 

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Yeah, they set it up exactly as I said above. Interesting that the guy that wrote the article also sells the boxes. He completely didn't mention the downsides to doing this and the requirement to eliminate time alignment in your front three channels feeding the boxes.


Next up you will be seeing articles on how to use one of those boxes to have a pair of di-poles and a pair of mono-pole surrounds next to each other. Depending upon the content have the surround info switched between them. Di-poles for the surround ambiance and mono-poles for stuff you want to localize.....


Shawn
 

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Chris,

" 1. "My work suggests that two sub-woofers is better than one"


Do you think this is true in most cases?"



It depends. If you are listening to monophonic bass signals, such as that contained in most pop recordings, then two subs are better than one only if you place them together, and they will only gain you bass dynamic range. If you are listening to material with stereo bass, which is admittedly rare, then two subs can be better than one, because of inter-aural time delay (ITD) effects in the bass, if you place the subs correctly. If you have discrete multi-channel recordings with discrete, non-mono (ie. non-correlated) bass in all channels, then full-ranges all around are good.


If you're using a Lexicon DC-1 v. 3.0 or higher, DC-2, MC-1, or MC-12, then two subs can be better than one on a lot of material, including pop songs, if you use Lexicon's Bass Enhance, which decorrelates mono bass.

" 2. "There is no question to me that a five channel front sounds

better than a three"


If this is true how would I go about implementing a five channel

front?"



This has been well-known since the 30s, but unfortunately, Dr. G was just talking in the theoretical. If you're handy with DSP programming or analog circuits, and linear algebra, Michael Gerzon describes ways to derive as many channels as you wish from two channels, while preserving and enhancing important psychoacoustic cues, ie. a multi-channel front array with a matrix that doesn't sound bad. Meridian's TriField system uses the 3-channel version of Gerzon's work.

" 4. "My ideal speaker configuration is five front, four in the rear, two in

in the ceiling. the five front being left,left center,center, right

center and right.


Do you think this is over-kill?"



No. 5.1 was a codification of existing theater practice when it was first introduced, and is basically the bare minimum configuration to get decent surround. Looking into the research in this area, you will find estimates of 12 to over 1 million (yes, one million) channels necessary to recreate a perceptually-useful soundfield, ie. a soundfield that humans can extract most of their perceptual cues on.

" 5. "All these extra channels can be matrix-derived so the only

discrete encode format you would need is 5.1"


What are your thoughts on this?"



As one of our AVS members is so fond of reminding us, Ambisonics does it with only 4 channels, albeit encoding only a single point in the soundfield. 6 full-range channels should be more than enough to deliver a perceptually useful soundfield, if the right encoding is used. It's not perceptually complete, as the 1-million channel system would try to do, but it would give use more cues to hang onto.


--Andre
 

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Quote:
There was an aritcle written by "Widescreen Review" that discusses this issue in some depth. They provide a relatively simple solution for creating additional matrixed front channels from the existing three channel array, as well as extracting the infrormation for the five front channels from Sony's SDDS format and the Todd-AO format.
Far be it from me to dissuade anyone from experimenting but this "solution" will create more problems than it will solve, making it not really worth the effort.


When a SDDS soundtrack is mixed down from its theatrical presentation of 5 channels across the front to 3 channels for home listening, the 2 additional channels (left-of-centre, right-of-centre) are not discarded but instead folded into the remaining 3 channels. However, and this is most important, in the mix-down those 2 additional channels are NOT distributed evenly into the other 3 channels; they are split with 1/3 of their energy going into their respective front L&R channels and 2/3 of the information mixed into the centre channel. This makes sense as these are additional "screen channels", heavy on dialog content. However, here's the big problem: the matrix decoder add-on box is looking for information (as front steering of all matrix decoders do) that is EVENLY split between the the 2 channels it is processing. So if you add a pair of these boxes between your centre and front speakers, you WILL generate an extra pair of channels but you WON'T recover the original SDDS channels. What will you get in those 2 new channels? Your guess is as good as mine.


What's worse is that the add-on box being described in the Widescreen Review article uses Circle Surround processing to extract the extra channel. Unlike most matrix decoders, which extract a centre channel and then cancel that information from the other 2 channels, Circle Surround extracts a centre channel but leaves the other 2 channels unprocessed (which was one of their selling points originally). This is a recipe for disaster across the front speaker array, as the sounds you'll hear from the 2 new channels will still be coming from their original channels. I've heard of people using add-on boxes to get additional surround channels and, while I still don't think it's a good idea, any problems it might create won't be as audible in the rear hemisphere; especially if the surround channels contain mostly ambience information and not discretely placed effects. However, it IS a bad idea to apply this mess to the front channels; this is where our hearing is at its best & most acute and where soundstage imaging has to be most critical.


Also keep in mind that SDDS's 5 channels across the front is designed for environments that are large enough where using only 3 speakers might leave you with holes; i.e., a 50 foot wide screen in a commercial movie theatre. In fact, many multiplex theatres don't use all 5 front channels for their smaller auditoriums; the SDDS decoder takes the two additional discrete channels and folds them into the remaining 3, using the two-thirds/one-third spread described above.


BTW, I have no problems with additional channels/speakers for home use. In fact, the more speakers you use, the less you need to rely on phantom imaging; always a good thing. So if you had a big-screen rear-projection television, I can imagine having the 2 main speakers placed wide apart, the centre channel on top of the TV and 2 additional speakers placed directly on either side of the TV or on the very outer edges of the top. Having 3 screen channels will allow you have panned dialogue and other screen specific sound effects; this could be really cool when actors walk across the screen and the dialog follows. However, effects like that have to be specifically mixed and then encoded into the soundtrack for proper recovery; not the hack job that the Widescreen Review article is advocating.


Finally, there are other reasons to be wary of that article and the scheme it is recommending. Shawn pointed out some of them, but I'll underscore his comments. The author: this is the guy that's actually selling these boxes and, coincidentally, had a sale after the article was published where if you bought one box you could buy another at half price (the ad specifically quotes the article and how you can use the second box). He also never mentions ANY potential problems that can occur with this set-up; this is the difference between a marketing brochure and an article that aims to inform. Bass management: if your front L&R and your centre are set as different sizes (as most people's are) in your processor, what size does that make the 2 additional channels; i.e., what is their crossover point? Volume level: If your fronts and centre have to be adjusted to different relative volume settings (as most people's are), where does that place the volume setting of the 2 new channels? Time alignment: if your fronts and centre are at different distances from you (as most people's are) and you use time alignment to correct this, you are going to get problems when combining 2 differently timed signals. This why bass management is done BEFORE time alignment, in order to avoid any weird re-inforcements & cancellations and muddying of the signal that can occur when combining information (in this case, the bass) from channels that have individual time alignment applied to them. Speaking of which, since these channels are not generated by your main processor, there is no way to apply individual time alignment to them; nor bass management; nor volume level control; etc. You get the idea.


Best,

Sanjay
 

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Sanjay,


Good point about the volume. I would think you would need the volume level into the decoder to be the same for the L/R and center. Otherwise the volume difference might trip up the decoding as I believe they look at phase and level. So you would need some way after the decoder to then handle relative volume level adjustment for all five channels.


"you are going to get problems when combining 2 differently timed signals. This why bass management is done BEFORE time alignment, in order to avoid any weird re-inforcements & cancellations and muddying of the signal that can occur when combining information (in this case, the bass) from channels that have individual time alignment applied to them. "


While this is completely right when we are talking about combining channels (such as with a mixer or something like the ICBM) this wasn't the point I was trying to make. The problem here is actually much larger.


In a nutshell the decoder looks for any in phase (and level) material between say the L and C channels. It routes that to its output which becomes the left center speaker.


If you apply time alignment to the signal and it is different between L and C you are actually altering the phase between L and C. Now the stuff that would have been in phase between the two is *not* in phase and wouldn't be routed out to the Lc. In effect what you would want to go to the Lc won't and what will will depend upon how much the time alignment is altering phase between the channels. IOW... it is a mess.


Shawn
 

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Quote:
Originally posted by Chris Bone
What are you differentiating when you refer to your Left sub, right sub and then your LFE?
The MC-12 differentiates between DERIVED bass and DISCRETE bass. Derived bass is information that is low-pass filtered from other channels; discrete bass is information that already exists in a discrete bass track on the recording (i.e., the .1 LFE channel). The derived bass channels, which the processor creates, are sent to the SUB outputs; the discrete bass is sent to the LFE output. (Of course if you don't have a sub dedicated to LFE duties, that information can be folded into the SUB outputs.) The stereo sub outputs on the MC-12 derive bass from their respective sides: bass from all the left channels is sent to the left sub and bass derived from the right channels is re-routed to the right side sub.
Quote:
Originally posted by Philip Brandes
Moreover, your quote is incomplete, and misses a key point Dr. Griesinger was making in that interview: such a configuration would only be beneficial in the case of highly absorbant ceilings that remove the spatial realism of height reverberations--with hard reflective ceilings, the speakers would not be necessary.
Even with hard reflective ceilings, I think height channels could come in handy. If and when such a configuration does come into being, having the height information and/or reverberations as an adjustable parameter can give the listener the impression that he is in a larger space; not to mention being used for specific placement effects in movies.


Best,

Sanjay
 
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