adamdea;656596 Wrote: > > I mean for heaven's sake we know the data is sampled at a sample rate > of 44.1kHz, so why can't the data simply be decoded with a clock at > that rate? Only becasue of a possible over-underrun of data: does that > sound like an insurmountable problem? > > Basically as you point out you can/do have a new clock in the dac which > simply has to match the long term average rate of the transmitting > device. > No, it's not that simple and this is also why SPDIF was originally designed as it is. The problem is that there is no such thing as a "44.1 kHz" clock. You have a clocking device in your source and your DAC and both will have a frequency of 44.1 kHz +/- some deviation and two such devices will NEVER have exactly the same frequency.
So as a result, when you re-clock you will inadvertently either run into buffer under- or overruns. What do you do with these then? You have to either insert pauses or drop parts of the audio which IS an altering of the signal. Pauses might in theory be a bit more simple because you can insert them between tracks if your buffer is big enough but then the bigger your buffer the longer the delays you induce into the signal path and that, in turn, will kill things like multiroom-syncing. This whole topic is NOT trivial so the choice the SPDIF designers took was to use one clock throughout the signal chain and they chose the source's clock. With hindsight it might have been better to use the drain's clock because that's the part that does the D/A conversion so in a system tuned for quality it's the part that needs to be good so will have to have to most accurate clock. The Transporter, for example, compensates for this by allowing the use of an external clock source. > > I think that John Swenson's pojnt is that errors or noise before the > reclocking will still somehow modulate the Dacs own clock. Errors: yes. Noise: no, not if the DACs designer has any idea about his profession. Too much noise before the reclocking and a small buffer can lead to errors behind the buffer, though. -- pippin --- see iPeng, the Squeezebox iPhone remote and *New: iPeng for iPad*, at penguinlovesmusic.com ------------------------------------------------------------------------ pippin's Profile: http://forums.slimdevices.com/member.php?userid=13777 View this thread: http://forums.slimdevices.com/showthread.php?t=84742 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
