Mike,
This clock imprecision is indeed a known and documented issue. Squeezebox1 uses a "black box" DSP processor from a third-party supplier. It is a great mp3 decoder and has a lot of good features, but it also has a couple of irritating limitations like this that power users might encounter. While this off-the-shelf DSP was immensely helpful in getting us to market, unfortunately we have limited access to its internal workings, and next-to-zero support from the supplier, so this s/pdif issue has remained open for a long time.
Ideally what I'd like to have is separate, dedicated, high-precision crystal clocks to generate the DAC's clocks and the s/pdif carriers directly (no PLL), plus full software control of the s/pdif data and framing. This would yield VERY precise s/pdif clocks, eliminate the possibility of certain nearly-impossible-to-fix bugs, and ensure that we can reliably deliver bit-perfect streams for DTS and such.
Sean
On Mar 3, 2005, at 8:21 AM, Mike Reeve wrote:
Hi
Regarding problems with lock on external DACS ...
About a year ago it was found that the Squeezebox digital output was somewhat off 44.10KHz BUT ... ... Sean quickly [as usual!] fixed this in the firmware.
Fortunately I have always routed Squeezeboxes via a
device that buffers the input in a FIFO
and then clocks it out using its own high-precision, lower jitter clock,
so any such inacurracy has never been a problem for me.
However, out of curiousity I yesterday connected a Squeezebox to an Apogee Big Ben and it registers the Squeezebox at 44.13KHz :-O
[Another long-term issue has been the long settling time of the clock when switching into 'PCM mode' so I left the Squeezebox on repeat all night so that this was not an issue ...]
So, I'm wondering why the 44.13KHz:
(a) Has the firmware changed?; (b) Is this 'manufacturing variance'? :-O;
(c) ...
Clearly 44.13KHz is way out of the range of some 'high-end' DACs (e.g. AudioSynthesis DACs have a capture window of only +/- 100ppm - approx. 4Hz), so this could be the cause of some peoples' lock problems.
I know other people who read (or at least read) this list (such as Michel, Harry & Victor from the TacTHackers group) have both Squeezeboxes and Big Bens - what do you guys (or anyone else having the two) see as frequency these days ...?
Regards
Mike
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