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Music servers and other computer based digital audio technologies.

It's not a simple matter

If the streamer is sending USB it has a clock that generates the 8 kHz packet timing. This clock affects when packets are sent and hence when packets get to the DAC. If this clock is erratic than packets will arrive at the DAC at varying times.

In theory with Async USB the effect on this will be minimal, because of the buffering. Even if the average rate drifts out, then the buffer will start filling up more or start emptying out. Long before this creates a problem, the async protocol will send a message to adjust the number of buffer samples. Also, in theory, data will be clocked out of the buffer by a separate local clock, and this is the only clock that will affect the timing of the audio samples.

In practice, any changes in the clock in the source and other changes in the USB cable will affect the timing of events in the USB receiver circuitry in the DAC. This will be true even if all the same feedback signals are generated. The exact timing of current consumption will vary. There will be details of how buffering in the memory buffer work and with different timing of memory loads there may be different timing of memory reads. If the output of the memory buffer is reclocked using the DAC's master clock in theory any timing variations would not matter, in practice they may.

If you feed a different signal into the DAC (even with the same bits) it is reasonable to expect that you will get a different signal out. Ideally, the difference will be perceived as "small". In this case, it would be a waste of money to have sprung for a more expensive clock in the streamer. However, in the real world, the differences may not be "small" they may be "moderate" (and some enthusiastic audiophiles would call these differences "huge"). So it is entirely possible that going for the more expensive clock in the streamer may be worthwhile.

However, it is also possible that streamers with identical circuitry with the same quality clock may still sound different, if the streamer clock sends packets at a slightly different speed. This will affect the logic of the async USB receiver in the DAC. With different logic sequencing the DAC may sound different because of different internal noise generated by the USB receiver circuitry coupling into the analog circuitry.

In other words, you can't predict what is going to happen. In the end the decision would seem to be more affected by the size of one's wallet and the hassle factor of swapping components until one is happy.

If you want a serious headache, consider that the clocks may be operating more or less harmoniously frequency-wise as a function of temperature. This means that the system may even have good days and bad days. If you play the same recording twice the DAC may not produce the same output. After repeated listening the listener may be come completely confused, not able to decide whether everything sounds the same, sounds different, or if the listener is going crazy. :-)


Tony Lauck

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


This post is made possible by the generous support of people like you and our sponsors:
  Atma-Sphere Music Systems, Inc.  


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