lork;300871 Wrote: > Normal USB-DACs don't- they run "asynchronously", with a PLL to keep the > output bitrate at a speed that matches the incoming packet rate, so that > the buffer never over- or under-runs. This results in timing jitter, as > the PLL servos the output frequency back & forth to accommodate the > not-very-precisely-timed computer packets. I'm afraid you have this backwards. The whole idea of an asynchronous interface is that there is NO connection between the incoming data rate, and the outgoing. An asynchronous interface does not require a PLL, and if properly implemented, will not transmit jitter from the incoming stream to the outgoing.
A SPDIF connection is synchronous, and requires a PLL to extract the clock from the data stream. This type of interface has the potential for noise and jitter in the incoming data stream to affect the PLL's output jitter. lork;300871 Wrote: > It would appear that the Slim system could get around this, since they > have their own hardware & software. Hence there would be no real need > for re-clocking equipment between the Slim device and your DAC, since > the real culprit in timing jitter is that asynchronous feed & PLL > follower, not the inherent jitter on the oscillator (which is usually > extremely low). The Slim system is totally asynchronous. The data arrives in packets over the ethernet, and is loaded into a memory buffer, and then clocked out by the main system clock (which is not a pll). When the buffer gets low, the hardware requests a new packet and thus ensures it never runs out. As such, the total jitter is the sum of the Crystal controlled clock, and the associated clock distribution (pcb traces, glue logic etc), which can be tightly controlled. While this holds true for the slims internal DAC, as soon as you go outboard, via the SPDIF interface, your external DAC must use it's clock recovery circuit and PLL to re-generate the clock. So the potential for increased jitter exists once again. Is a re-clocker required with an SB3? I'd say no, it's inherent jitter is very low, so unless your external DAC has a poorly designed clock recovery circuit, it shouldn't be necessary. The jitter from a transporter is even lower, but it's DAC is very good, so there's little reason to go outboard. Cheers, Dave -- DCtoDaylight ------------------------------------------------------------------------ DCtoDaylight's Profile: http://forums.slimdevices.com/member.php?userid=7284 View this thread: http://forums.slimdevices.com/showthread.php?t=47491 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
