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RE: How can USB performance impact audio quality?

It should be possible, given the right clock architecture, to do this at a cost which is still less than the absurdly complex (and ineffective) band aids people try to apply inside their computers, software and/or hardware kluges or the cost of boutique transports and cabling.

Your comment about separate power supplies is on the mark. It may actually require more than two if it turns out that multiple stages of isolation are needed for best sonic results. However, with the right interface there is nothing particularly complex about the isolation interfaces, no protocols, just buffers and registers. The various stages of isolation can, and should be, within one clock domain shared with the DAC. The async USB receiver exists in two clock domains and has the necessary synchronizers.

This needs to be approached as an engineering problem. One wants to specify how many dB any (still bit perfect) variation on the input signal must be attenuated before it exits the DAC through the analog output. A good start would be to require that the difference between all recognizable eye patterns be attenuated to the point where all audio signals are affected by less than, perhaps -140 dBfs. (This does not mean that the output result has to be perfect to 24 bits, 1 psec jitter, etc., just that the differences in output caused by different input waveforms are attenuated this much.) This can be accomplished by multiple stages of attenuation, at the cost of very little logic per stage and the greater cost of separate power supply and packing for each stage. It seems likely that more than one stage of isolation may be required to reach this level of isolation. However, it is clear that each stage will provide some isolation, so there is no magic involved in adding stages as needed.

It should be pointed out that with multiple stages of isolation as one moves down the pipeline closer to the actual converters the quality of the components involved has to improve, i.e. all of the parts in the final circuitry, clock included, have to be audiophile grade. This is not necessary upstream after some stages of isolation. So the cost of going multiple stages may not be as great as it appears at first glance.







Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar

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