Subject: Re: [linux-audio-user] Re: Firewire, what's the story?
From: Mark Knecht (markknecht_AT_comcast.net)
Date: Tue Dec 09 2003 - 15:40:39 EET
On Tue, 2003-12-09 at 04:01, Clemens Ladisch wrote:
> Both USB and 1394 transfer the data in packets (and the packet could
> arrive near the end of a frame), so it must be buffered in the device
> anyway. Consequently, this jitter does not appear in the data fed to
> the DAC.
>
Please remember that the clocks that are driving the DACs will be
unsynchronized. If PC #1 plays a 44100Hz file, sending data at 44099Hz,
but the receiving PC #2 is trying to generate analog from this and its
clock is running at 44101Hz, then problems will occur.
This is overcome in 61883 since the receiving device is using the clock
embedded in the data stream to reset it's PLLs and getting synchronized
with the transmitter.
There is no way (that I know of) to get a PC's 1394 clock to do this.
All the OHCI controllers I've seen just use a fixed crystal source and
it's not tied to the clock on the sound card anyway.
To generate audio on the remote PC I think the clocks must be
synchronized...
- Mark
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