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Triode
2004-10-22, 11:30
Mark,

> The digital stream out of my Squeezebox seems to be running at slightly
> the wrong speed.  My DAC has three lock settings -> call them wide,
> narrower and narrowest.  Whereas a good CD transport can be locked
> onto at any of the three settings, the Squeezebox can only be locked onto
> at the wide setting.  From the specs of my DAC this suggests the
> clock of the Squeezebox is more than 100ppm out and probably even more
> than 200ppm than the DAC expects for 44.1kHz sampling.  To clarify, I
> rip full resolution wav files and store and unpack using flac. 
> Therefore I am outputting Redbook from the server to the Squeezebox, and
> again Redbook out of the Squeezebox.  The DAC recognises the input as
> being 44.1kHz -> ish, but not close enough to use any lock setting than
> its adaptive rate setting

This is a subject that interests me as I am an audio diyer and plan on
modifying my DAC to use a crystal locked reclocking circuit.

Appart from the time to reach a stable frequency - could it be that the
stable frequency is outside the capture range of your dac? These are often
implemented with a crystal based oscillator with ~100 ppm capture range and
a feedback mechanism to adjust it to lock on (ie. a crystal oscillator based
PLL).

If so it looks to me that the server code could be modified to alter the
output frequency in essentially 1/18432 kHz steps [or actually that *48/44.1
for pcm] The current pitch adjustment doesn't work for pcm as it makes the
center frequency 48 khz and adjusts in big steps (caused me to scratch my
head when I first tried it!) However with a few minor mods to the server
code I suspect it is possible to alter the frequency in small steps.

Send me a mail off list if you are interested in discussing - I'm happy to
propose some server changes but don't currently have a DAC which is fussy
enough to test against.

Though as noted before, its very possible it is the time for the speed to
stablise rather than absolute speed which is the issue.

Adrian

Michel Fombellida
2004-10-22, 15:29
Hi Triode,

FYI: I am currently in contact with a tweaker who is looking at adding a word
clock input to the SB. I'll post here when he has completed his investigations.

Michel