What is 7 channel sound?

[sonny]

I am reasonably well clued up on this subject generally but can someone explain why the current crop of receivers have seven internal amplifiers?
My amp is a Sony STRDB1080 with true 6.1 decoding, and I understand this potential is only truly fully used on a discrete 6.1 DTS ES track such as Balde 2. Dolby Digital EX uses a 'matrixed' surround back channel.
So to return to my question why do some amps now have seven driven channels? Which channels are being employed and which surround formats are these aimed at?
Is there a significant advantage to be gained?
Thanks,

Common misunderstanding this one, do a search on 7.1 and you'll find quite a bit of discussion on this subject.

Basically, as far as software is concerned the most advanced available is 6.1 discrete. You could run two speakers off your sixth output terminal to get "7.1", or you could get an amp that has seven amps and so each speaker has it's own dedicated amp and the performance is improved. Both options still give you 6.1 sound but it's called 7.1 because you've got 7.1 speakers. Bit misleading because the signal coming from the 6th and 7th speakers is exactly the same. Having two surround backs does beef up the performance a bit. Also, many 7.1 amps have various matrix or DSP modes some of which claim to offer a matrixed 7.1 mode created from a 6.1 soundtrack.

7.1 amps are also a bit more future proof because they have an 8 channel input which could be used with a DVD player with on board 7.1 decoding and an 8 channel output in the future if and when true 7.1 ever becomes available. This is similar to how a pro logic amp with a 6 channel input can be used with a DVD player with on board DD/DTS decoding and a 6 channel output to give you 5.1 sound, even though the amp doesn't have 5.1 decoding on board. However, by the time true 7.1 ever becomes available, if ever, there will be so many other bells and whistles around that the current crop of "7.1" amps will be obsolete anyway.

If you are curious about seeing how 7.1 compares to 6.1 you could hook up another surround back speaker to your 6th speaker terminal, be careful how you do this though, maybe someone else can advise if this is safe or not. Or maybe you could buy or borrow a stereo power amp and hook it up to the 6th channel pre out and so you'd then have one amp per surround back speaker - again maybe someone else can advise whether or not this would work. I've not tried either of these options as I just went straight for a 7.1 amp, only after pruchase did i find out that there were no 7.1 DVDs.

Hope this helps.

The relevant question for those who have existing '7.1' systems is if and when discrete 7.1 soundtracks become available, would their DTS-ES Discrete decoder be able to decode such soundtracks. From your post, you seem to imply that this would not be possible (since analogue 7.1 multichannel input should not be regarded as 'de facto' 7.1). From what I understand of DTS decoding technology, the implementation of the DTS-ES Discrete decoder takes advantage of the design flexibility of the DTS Coherent Acoustics codec, which has been developed to allow modifications and updates to new encoding technology (such as discrete 6.1 on the encoder side) but was also designed to keep the decoders relatively simple and thus future-proof. This goal is accomplished by putting all of the "intelligence" of the Coherent Acoustics codec on the encoder end, with the decoders merely following instructions embedded in the audio stream. At present, DTS-ES Discrete 6.1 encoding is performed by DTS using software-based encoding systems. I think this implies that should DTS release discrete 7.1 soundtracks, the present DTS-ES Discrete decoder can indeed decode them, but only if the algorithms allow it. In other words, the future depends on DTS allowing this development. However, they could also be cynical and produce 7.1 soundtracks in such a way that only new 7.1 decoders can decode them, hence forcing av amplifier manufacturers to install new and expensive decoders in their units.

reservoir51

[sonny]

Thank you for your comprehensive explananations.