On Thursday 22 November 2007 21:01, Vladimir Mosgalin wrote:
> > I meant "M-Audio Revolution 7.1, and quite possibly M-Audio Revolution 5.1
> > allow you to use external clock source.
>
> In theory, yes. In practice, I wasn't able to make my M-Audio Audiophile
> USB get clock from external source. Well it kinda works, but at some
> point distortions appear, and one must force clock resync or something
> like that by turning card off and on.
mmh... I guess the USB interface may be the problem source here.
Though USB could be operated in asynchronous mode, AFAIK most (all?)
of the current USB audio devices operate it in synchronous mode, with
the clock provided from the PC.
Of course, if the USB interface (from which the digital audio stream
is coming) is operated synchronously with source-based clock, then the
sound card MUST be somehow in sync with that stream clock...
The only way to "loosen" the sync with that clock and try to sync to
another one is to do some sort of reclocking, but unfortunately that
is not gonna work quite well.
In particular when the "upstream" clock is that of an USB connection
which - apart from being usually "dirt" and not so stable - is at odd
rates with respect to audio clocks.
The only real solution would be a sound card which connect to the PC
through an _asynchronous_ interface (be it USB, firewire, Ethernet,
HDMI or whatever else, as long as it's fast enough and asynchronous).
BTW, do you know if any such device exists?
> I wanted to create setup similar to this, and one of the things I learned that
> in order to reduce jitter, you'd want to have power as clean as possible.
indeed, absolutely.
> On-board soundchips produce lowest quality signal, pci/pcie boards have much
> better filtering and produce better signal, but if you want something better,
> you have to use card which isn't powered by PSU of your PC, and doesn't suffer
> from problems of its signal. So if you want best digital audio, you probably
> should look among external cards (usb/firewire) which aren't bus powered, and
> use external AC adapter. Interface doesn't matter as long as card doesn't get
> power from it, so choose most compatible card.
well, I have to disagree here. Interface would/should not matter
ONLY if it is asynchronous.
If the interface is synchronous, then the card has to lock itself
to the interface clock and, unfortunately, IMHO/IME no reclocking
and/or resampling will ever be able to really clean up the mess.
For the USB, the standard bus clock frequency makes things even
worse... don't know about firewire.
Ciao,
Paolo.
--
Skype: Paolo.Saggese
http://borex.lngs.infn.it/saggese
You can still escape from the GATES of hell: Use Linux!
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