View Full Version : Modifying squeezebox clock

Julian Alden-Salter
2005-03-02, 04:11
This is the stuff I found on audio synthesis' website...

Following input selection two PLLs are used to extract and purify the word
clock. An electrically and mechanically isolated crystal oscillator forms
part of a sophisticated second order PLL, tightly bandpass filtering the
recovered clock before applying it to the digital filter and DACs. A third
digital loop is used to isolate jitter generated in the digital filter - all
DAC loading and sample & hold timing is derived from this third digital PLL.

Inputs are reclocked on multiple occasions before reaching the DAC itself.
Low frequency jitter is the most difficult to eliminate so the three PLLs
have been carefully optimised to boast a sub 1Hz jitter cut off frequency
With the aid of multiple PLLs and intelligent muting we have made locking to
jitter-ridden or off frequency transports routine, whilst maintaining
automatic silent crystal locking for higher quality sources.

From here: http://www.audiosynthesis.co.uk/dax_decade.htm

So much phlogiston to me though.

I've actually upgraded recently to the decade from a dax-2 from the same
company - this previous dac also exhibited similar behaviour with mp3 /

I take on board the buffer stuff phil mentioned but I don't get stuttering
and can't see how an intermittent buffer underrun would cause the dac to
fail to xlock (crystal lock from above).



-----Original Message-----
From: Sean Adams [mailto:sadams (AT) slimdevices (DOT) com]
Sent: 02 March 2005 05:09
To: Slim Devices Discussion
Subject: [slim] Modifying squeezebox clock

On Mar 1, 2005, at 8:08 PM, Phil Karn wrote:

> Julian Alden-Salter wrote:
>> 1) The fact that my dac locks on with different qualities of lock
>> when mp3
>> and flacs are played back. Suggesting that there is indeed some
>> difference
>> in the spdif data stream between the two formats.

There is a "just for your information" bit for clock precision in the
s/pdif channel status data - that may be what it is. If so, it has
nothing to do with actual clock precision, it's just a bit that says "I
think I'm a high precision clock" or not. I'm not sure what we send
for this bit but I could check it on my analyzer - at any rate, it does
not affect functionality/performance in any way.

Does your receiver (maybe in the instruction manual) say exactly what
it's reporting?