In Reply to: Isolation? posted by fmak on July 30, 2015 at 13:09:51:
Isolation does not improve sound quality. It removes deterioration in sound quality caused by extraneous noise. If done successfully, sound quality will not change with changing bit perfect digital sources, but that's not enough. The constant sound quality must also be excellent.
As you correctly point out, some of the isolator circuits may remove external noise, but generate their own effects. They have to be reclocked, or more precisely buffered in a flip flop or shift register and some fancy footwork needs to be done with the clock phases. It's possible to design a shift register that will attenuate the variations in signal level and timing by buffering, and were it not for power and ground leakage, this could be made arbitrarily large through adding additional stages to the register. However, once the effect of power and ground come into play the idealized circuit and transistor design meets physical reality. Some of the isolators have ugly RF modulators in them, to generate an AC signal that can be sent through some kind of isolation network. I suspect that a better approach is to eliminate the DC component by using Manchester code. The Manchester encoders and decoders require a minimum of digital logic and can use readily available pulse transformers. Several stages of "isolate and then buffer/reclock" can be repeated if needed. But note that there isn't really any reclocking because all of these stages are synchronous with the main DAC clock.
One thing that's nice about DSD is that there are no clock signals that are running anywhere near the audio band, provided that everything can be kept streaming. (No damn packets or pseudo PCM format kluges.) So in this case, the interconnect is more akin to the SDIF variations. I see no need for a DAC to do anything but accept DSD at one suitably high rate. This further reduces the amount of digital logic that is anywhere near to the critical mixed signal and analog circuitry and all the circuitry can be tuned to one sweet spot.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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Follow Ups
- RE: Isolation? - Tony Lauck 07/30/1514:08:14 07/30/15 (4)
- RE: Isolation? - soundchekk 02:09:09 07/31/15 (2)
- RE: Isolation? - Bob_C 10:14:53 07/31/15 (1)
- ANother - fmak 00:00:25 08/1/15 (0)
- DSD - fmak 23:45:45 07/30/15 (0)