Hi SS, yes we're talking about reasonably high quality audio - so it's 96kHz/24bit, 192kHz/24bit, etc.. Note that 17B assumes that phase distortion caused by anti-aliasing filters is minimal within the "in-band" - generally a reasonable assumption (compare this to the vast quantities of phase distortion caused by the "brickwall" filters in 44.1kHz/48kHz systems). Note also that the maximum frequency generated by musical instruments can exceed 100kHz, and the temporal resolution of the human auditory system is typically 7 us or better - this also has implications for required sampling rate.
Nevertheless, taking 17B and B as 20kHz as a reasonable minimum gives a sample rate of 340kHz. 24 bits is the current consumer standard - but then again whilst many Hi-Fis can sound painful not many can take you beyond the threshold of pain. ... but if we're really talking fidelity, transient response, etc., certainly a few more bits would be good. Coincidentally, Intel's current PC audio standard (HD Audio) supports up to eight channels at 192kHz/32bit.
As you'd expect from 17B, 192/24 sounds much better than 96/24, ceteris paribus, whilst 384/24 sounds much better again, with higher rates sounding even better again ...
As far as number of channels is concerned, current surround sound is not true stereo, but forms a ring of sound - instead of a three-dimensional soundfield. True stereo using a dozen or more drivers placed around the room (including G_d speakers above and floor speakers below) and probably including beam-forming/steering technology, as required.
Based upon current technology I guess we're talking maybe 16 channels of 384kHz/24bit - around 150Mbps. Of course, there's plenty of lossless redundancy in there, and entropy-based compression can be used to get it down to around 12Mbps, and Blu-Ray's 54Mbps/72Mbps capabilities could be used with a 50GB disc to give HD video and superb audio simultaneously - imagine a concert on that!
.. and of course, DSD's (SACD's) 2.8224MHz/1bit system could be seriously upgraded as a viable alternative to 384/24 and higher ...
When you see the figures it's not surprising that the brain devotes almost as much processing power to audio as it does to video ...
... and where does 17B leave the perfect sound of (16bit) CD? ...
|