John Rigg ha scritto:
On Mon, Sep 17, 2007 at 08:44:03PM +0100, John Rigg wrote:
On Mon, Sep 17, 2007 at 12:22:19PM +0200, Ludovico Verducci wrote:
Hello all!
I'm developing a complex multichannel audio distribution system where multiple linux boxes will stream audio data over ethernet and then should play audio at sample level resolution synchronization. The boxes clocks are synchronized over ethernet using PTP. I need to keep in synch the audio board's clocks and I can't use an external wordclock nor s/pdif.
Won't this cause serious clock jitter problems? I don't see how the PCI bus can deliver precise enough timing, considering how much other data it has to handle.
I didn't mean to directly drive the audio board's clock over the PCI bus. I think this is simply not feasible. But I think that using control signals periodically exchanged over PCI between the audio board and the kernel could be possible (if the hardware could support a similar feature, of course) to skew the board's clock to keep it in synch with a software reference. As far as I know the delta family boards drivers support the synchronization of up to 4 audio boards over PCI: at the moment I'm reverse engineering the hardware trying to understand how this can be accomplished.
And I can't see any way that the clocks can be synced to sample accuracy over ethernet. That's what external word clocks are for. Even with a word clock I suspect that the latency of the ethernet connection would be too high to allow sample accurate sync of the audio.
John
The machines real time clocks are synched over ethernet using Precision Time Protocol. This protocol can achieve below 1 microsecond synchronization accuracy. This should be fine to sample level synch at 48 KHz.
Regards,
Ludovico