Re: [Alsa-user] "best" card for "bitperfect" SPDIF I/O with external clock sync ?

[Paolo S. <pms...@ya...>]

On Wednesday 21 November 2007 23:49, Bill Unruh wrote:

> The clock jitter tends to be in the ppm range. This means that the
> frequency jitter is very low (if I believe the ppm then at the level of -120dB) 
> which is completely inaudible. My cheap Transit card reliably gives me noise  

unfortunately, it's not as simple as it seems... in the real world,
with real (not ideal) DACs, jitter DOES matter, much more than you
can think. Even at ppm or ppb levels!

Nowadays there is plenty of documentation (and discussions) on the 
subject. Try googling for e.g. "digital audio jitter" if you want to 
know more (though the most interesting things are closed in the JAES
articles, sadly out of the reach of most people).

If the digital audio folks have had a lesser simplistic approach in
the first place, we would not have had to wait some 20 years before 
gettin' a barely acceptabe sound out of a CD... 

(what's worse is that, nevertheless, even now a good analogue system 
can still sound MUCH better than any CD: it actually takes a good SACD
or DVD-A system to come close to the good old LP when it comes to the
real perceived audio quality!)

> SPDIF is a digital output stream. Its "clock" is irelevant. The clock on
> the machine that converts that stream to analog is the important one.

unfortunately, SPDIF is a synchronous interface... go figure. ;-)


Ciao,
                                Paolo.

--
Skype: Paolo.Saggese
http://borex.lngs.infn.it/saggese
You can still escape from the GATES of hell: Use Linux!