shauns (11/08/82)
Whew! rabbit!jj seems to be really angry about the audio cowboying on the net. I fully agree with his opinions of digital-it is definitely superior to analog, independent of weighting curve. However, I believe the point being discussed was the ARTISTIC superiority of available digitally mastered disks, not their sonic superiority. At least, that's what I commented on. rabbit!ark (who is rabbit, anyway? Where is rabbit?) has brought up an interesting topic - distortion mechanisms in digital recording. There are some recording studios, Sheffield Labs most vocally, that eschew digital on the claim that its mid-to-high frequency definition and `airyness' (sp?) are inferior to analog. This claim seems somewhat suspect. dbx claims that analog mastering decks when used with the dbx system have a dynamic range of 120dB. Also, a sidebar article in a recent edition of Stereo Review enumerated some of the potential problems with digital, to wit: =the behavior of THD in the digital format is exactly opposite that of analog- THD increases with decreasing signal level because of the finite size of the LSB. However, for a 16 bit system this means that the signal would have to approach -60dB for a 3% distortion level. =0dB is 0dB on a digital system-period. There is NO headroom, or at the most perhaps 5dB if you accept 3% THD as the definition of MRL. This could be the cause of a lot of listening headaches. The digital recorder doesn't `round over' the peaks like an analog machine but hard limits them. This could throw a lot of HF(10-20KHz) Distortion products into the output-anyone who's listened to a tweeter breaking up knows the headaches it causes. But this is a problem of miking and mixing technique. =The extremely steep filter slopes used to keep the sampling rate close to Nyquist induce phase aberrations in the audio passband. If you use a crummy filter, this might be a problem. However, it seems to me that phase jitter between channels is more of a problem-and analog recorders have it much worse than digital. Secondly, can you actually hear 5 degrees of jitter? Perhaps the filter slope, if not steep enough, can introduce IM distortion- but is it severe enough to be heard? =Excessive code dropouts may be another form of irritation that is easily perceptible (speculation only!). As for `only' a 20KHz bandwidth, that's fine with me. It's dead flat out to 20KHz regardless of recording level-show me a home deck that can do that at MRL! One final thing-has anybody considered the truly marvelous universality of the DAD? ! Assuming a player that can take the vibration levels and is small enough, the format is sized to go from your home to your portable to your car. No more tapes eaten by vicious car decks! Riding the dynamic range, the old cowpoke, Shaun Simpkins tekcad!shauns
nrf (11/09/82)
Re: distortion at low levels with digital techniques: such distortion can be overcome by using an alternate coding scheme from straight PCM, such as Adaptive Delta Modulation, Differential PCM, Adaptive Differential PCM, or some representation with a exponent-mantissa format similiar to 'floating point'. N. R. Fildes, BTL Whippany
tony (11/10/82)
#R:tekcad:-25700:pur-ee:12000002:000:264 pur-ee!tony Nov 9 19:02:00 1982 By the way, my recent note which gave some theoretical SNR info related to quantization assumed PCM was used. If delta modulation, etc. is used, then better SNR figures can be achieved, REGARDLESS of the amplitude of the signal. Tony Andrews pur-ee!tony