This area gets confusing because of loose talk by both hardware manufacturers and users. But the question is about sound formats, so let's forget what the hardware makers claim they're offering and concentrate on the formats actually used in HT software today:
Dolby Digital and DTS (basic flavors): Capable of carrying up to five channels of audio (left, right, center, left rear, right rear), plus a Low Frequency Effects (or "LFE") channel. Hence the notation 5.1. (Note, though, that not all DD or DTS tracks use the complete array of 5.1 channels. Many DD tracks use just two.)
Dolby Digital Surround EX a/k/a THX Surround EX: People call this a "6.1" format, but it's not. It's still a 5.1 format, only the left and right rear channels are encoded so that a matrix decoder can extract a center rear channel.
DTS ES Matrix: DTS's version of DD Surround EX.
DTS ES Discrete: The only -- repeat, only -- true 6.1 format out there. The center rear channel is encoded as a separate track. If the mix is done right, it's also matrixed into the left and right rears so that all the sounds are there even if you have just a plain old DTS decoder. The DTS ES Discrete decoder does some fancy footwork to make sure you only get the discrete version, not the matrixed.
That's it. That's all there is. The rest is just variations created by DSP manipulation in receivers and pre/pros. Some of those manipulations are quite good (e.g., Lexicon's Logic7). But those are the formats to choose from.
There is no "7.1" format. Let me repeat that: There is no "7.1" format -- meaning no format with seven discrete channels of sound, plus LFE. People talk about it all the time, but it's a misnomer.
Michael- Ahhh, but I always think of it as what format the source is in, and then *also* what type of speaker set up is supported by that format.
For example, by your definition, DD EX is a 5.1 format. But, it supports a 6.1 or 7.1 speaker system. Same for DTS-ES (matrix). (While also being backwards compatible with 5.1 speaker systems.)
And, even though Logic 7 is not a "format" but a decoding algorythm, it genuinely "supports" a 7.1 speaker system. Same for THX Ultra2.
Same for CES by Outlaw and xS by Rotel. And for those 2 decoding algorthyms, you can "expand" from 2.0 through 5.1 sources to a 6.1 or 7.1 speaker system.
I have a technical question regarding this. While DD-EX is not technically a discrete channel, it is different from manufacturer specific DSP modes in that when the mix is put together, a sound engineer determines what is matrixed into the rear L/R for the center rear? Is this correct? i.e. DD-EX is not simply a standard DSP mode that everyone now supports - and actually involves work when the dvd is produced? Someone correct me if I'm wrong since i've been curious about this.
OK, so with any source, such as regular DD or DTS, or the 6.1 matrixed DD EX and DTS ES and the DTS Discrete, you can run 7.1 speaker format?
For instance, with the matrixed formats, you send a matrixed rear center or surround channel to 2 speakers? Same with DTS ES discrete?
It seems to me that 7.1 is just 6.1 with either two "centers" or two "rear surrounds".
Is this correct?
What I'm getting at, is that nothing is stopping 6.1 owners from using a Y-cable and splitting the rear center or rear surround channel into two speakers. Should work for whatever format, with of course, the best results with DTS ES discrete. But, using whatever format, be it ES discrete or matrixed, and provided you calibrate the levels, there shouldn't be any difference between a 6.1 setup with 2 speakers, or a receiver which actually has 7.1 channels. Correct?
CHris, that is how I believe it works. a 7.1 receiver is simply one that is sending the same rear center signal to 2 discrete amplified channels. One could simulate this by simplying sending the pre-amp rear center speaker signal out to another dedicated 2 channel amp I would guess.
Both Logic 7 and THX Ultra2 give you 7 channels of different info. The 2 extra rear channels are decorrelated with each other so it is not simply 2 mono signals back there.
I think that for Outlaw's CES and Rotel's xS modes, that you do get 2 mono rears if you have 7.1.
And for DD EX and DTS-ES, definately 2 mono channels back there for 7.1.