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RE: Is it possible that high system latency is the culprit - usually the main case of dropouts?

There is always the possibility that the computer is failing to supply buffers to the USB hardware in time, resulting in undrruns. However, if this were the case it would seem likely that the problem would not be affected by the DAC "exact" settings. With my Mytek I have a dedicated driver with a control panel that displays this and other kinds of buffer underruns. I have no idea if this kind of information is available on the MAC. (I can easily get buffer underruns by setting the buffering too low, overloading the computer, etc...)

Another problem can exist with async USB. Here the DAC is supposed to send feedback to the computer as to the number of audio samples to place in each frame. (The frame rate is 1 msec and is timed by hardware at the USB controller.) Given the DAC clock runs at a different rate than the computer clock it will be emptying its buffer at a different rate and there is a flow control mechanism that causes the data rate (audio samples) to be adjusted to try and center this buffer. If the buffering is too little or there is too much delay in sending new size info, receiving this, and processing it then the feedback may arrive too late for effetive correction. Depending on the details of how interrupts are handled (I don't know about Mac OS) various things in the OS can delay the processing of the necessary feedback, causing the buffers at the DAC to overflow or underflow. This would possibly explain why computer latency would matter with respect to the DAC settings.

The proper approach to this problem would be for a responsible manufacturer to investigate what was happening and why and take corrective action, which might involve making whole unhappy customers, updating the firmware or product design, or changing the marketing literature. Unfortunately, "business is business" and this may not happen.


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: Is it possible that high system latency is the culprit - usually the main case of dropouts? - Tony Lauck 02/16/1509:29:34 02/16/15 (1)
    • Good - fmak 22:25:44 02/17/15 (0)

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