Jack, on the part of your reply where you ask about possible bit rate(sampling rate is also another difference)differences making a difference in sound quality even where multi-channel isn't a factor, yes that's often claimed. This hasn't come up much recently and one of my
replies from three years ago still has some active links to good info. The poster "soundhound"(shown in his replies by his later boardname of "HAL 9000")explained how better recording, mixing and mastering made the difference that was often heard, not higher sampling and bit rates. He also pointed out that even on the same disc different mastering was often applied to CD and SACD layers, which could account for a difference.
When Sony and Philips were co-developing the CD format around 1980 they agreed to use a 44.1KHz sampling rate and 16 bits(Philips originally proposed that 14 bits were enough)as being more than sufficient for the frequency range of human ears and the dynamic range of the material that would be recorded. Since two digital samples exactly reproduce an analog waveform, 44.1KHz sampling exactly reproduces frequencies up to 22,050Hz, beyond audibility. Likewise, 16 bits provide for a theoretical maximum dynamic range of about 98dB(6.02n + 1.76dB), and actual recordings have at most 80dB of range(many almost uniformly loud pop recordings have a dynamic range on the order of 10dB).
So, while DVD-As/SACDs can sometimes sound better than CDs of the same performance, higher sampling and/or bits is unlikely to be a significant factor. Of course when the DVD-A/SACD has discrete multi-channel placement of performers in surround channels, this sounds different and hopefully better. On the other hand, where the surround channels contain only ambience information(most classical DVD-As/SACDs)rather than discrete performers, applying processing such as DPLII, Logic 7, Neo:6, etc. to CDs can provide a very similar result. I own one SACD and likely won't be getting any more.
