audioengr;147927 Wrote: > The crystal or crystal oscillator that drives the PLL is replaced with a > Superclock. It is still a PLL driven by a fixed frequency clock, but > the jitter contribution of the clock itself is reduced. > > Steve N.
OK, I'm not an electrical engineer, so probably this is a stupid question - but I still don't get it. As far as I understand, there is a PLL locked to a crystal oscillator in the CD player. The data stream coming from reading the disc will be jittery, as you're saying, and I suppose the output of the PLL could be sensitive to that and therefore jittery. This is the clock that controls the rate at which data is read into the buffer. However it's not clear to me why you would want or need to use this as the clock for reading out of the buffer or for the DAC. The point is the AVERAGE frequency of the PLL clock would have to be very very close to identical to the frequency of the crystal oscillator, or an integer multiple of it (based on the little I know about PLLs). So why would you use the output of the PLL as a clock for the DAC and/or buffer readout, when you could simply use the crystal itself? A problem (with buffer under or overflow) would arise if the AVERAGE frequencies of those two clocks differed, but I don't see how they could. So all you would need is a buffer large enough to withstand the variations due to the jitter of the input clock - and that's very very small. In fact naively it doesn't need to be much larger than one bit, unless the jitter is so bad it causes bit errors (in which case all bets are off anyway). So unless there's some reason you can't use the crystal as the clock for the DAC, it seems that the buffer insulates you entirely from jitter in reading the disc. Am I missing something? By the way, this has been a very interesting thread for me - I've learned a lot, and thanks to all that have participated so far. -- opaqueice ------------------------------------------------------------------------ opaqueice's Profile: http://forums.slimdevices.com/member.php?userid=4234 View this thread: http://forums.slimdevices.com/showthread.php?t=28621 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
