PhilNYC Wrote: > What remains a mystery to me is (as highdudgeon points out) that if a > DAC has a data buffer and a re-clocking mechanism, why would upstream > jitter have an effect? I still don't have an answer for that. >
I don't know the answer either, but here's a shot at it. Think for a moment about the buffer. It's not infinitely large - it has a limited capacity to hold data. If you recall that one CD is around 700 megabytes of data, you'll see that the buffer can probably hold at most a few minutes of audio data, and more likely less. OK, so what? Well, recall that there are two clocks involved here - the one on the transport sending the digital data into the DAC, and the one inside the DAC outputting data from the buffer to the DAC chip itself. Those two clocks are not running at the same rate (no two clocks will run at exactly the same rate - close, but not exactly). Think of the buffer as a bucket into which you're pouring water, while the water is draining out through a hole at the same time - but not at quite the same rate you're pouring. Eventually the buffer either fills up (if the transport clock is faster - I think that's called buffer overflow) or empties out (buffer underrun). So then what is the DAC supposed to do? I can think of a few possibilities off the top of my head, but none of them are without compromises. Ultimately it might be ncessary to switch back to the original transport clock when the buffer fills or empties, thus re-introducing jitter. So I'm not sure this bufferring/reclocking story is really the silver bullet people make it out to be. -- opaqueice ------------------------------------------------------------------------ opaqueice's Profile: http://forums.slimdevices.com/member.php?userid=4234 View this thread: http://forums.slimdevices.com/showthread.php?t=22301 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
