Hi All,
I have some further information regarding this problem. Late last year I was trying to get a freinds MK1 Audio Synthesis DAX to lock to my Squeezebox. We saw the same problem, A good lock with MP3 streams, no lock at all with FLAC.
The Mk1 DAX has a very narrow PLL clock capture window specified as +/- 200ppm.
(Verified by the designer of the DAX).
Subsequent revisions of the DAX product line have multiple capture windows to allow
locking to a wider range of transports, albeit at a lower quality.
The DAX2 has a dual stage lock window at +/- 200pmm and +/- 1000 (ppm). The wider lock windows have been reported as working.
With help from Triode I tried tweeking the programmed crystal value to try and find a
suitable lock (basically a modification to the pitch function) with no luck.
It is unclear to me why there should be a data dependent difference in SPDIF clock accuracy.
(In fact activating a DSP to perform MP3 decoding would seem to be far more likely to increase
jitter due to noise injection). The Micronas data sheet offers no insight that I can find.
Recently another friend reported the same lock issue with the latest model Cyrus DAC-X.
So it appears that this is not an issue confined to a single high-end manufacturer.
I can guarantee the sale of another squeezebox if this issue can be resolved !!
Neil
From: "Julian Alden-Salter" <[EMAIL PROTECTED]> Reply-To: Slim Devices Discussion <[email protected]> To: "'Slim Devices Discussion'" <[email protected]> Subject: RE: [slim] Modifying squeezebox clock Date: Wed, 2 Mar 2005 11:11:31 -0000
Hi, 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 / pcm/flacs.
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).
Cheers
Julian.
-----Original Message----- From: Sean Adams [mailto:[EMAIL PROTECTED] Sent: 02 March 2005 05:09 To: Slim Devices Discussion Subject: Re: [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?
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