On Sun, Apr 26, 2015 at 10:55:42AM +0200, Anders Genell wrote:
> [....]
> 
> As you say, Pete, using NTP should be possible in some way. If e.g. having one machine regularly synching its system clock to an official NTP server, and setting it up as local NTP server and having the rest of the machines synch to it, it should be possible to keep the system clocks in good synch.

This is sort of what I was thinking.

> So the question is how to sync an audio stream to the system clock? Does the audio stream have to sync to a sound card clock? Can the sound card clock be synced to system clock? Can the (recorded) stream be synced to the system clock independently of the sound card clock?

I hadn't considered this!  I guess most (all?) audio cards have their own sample clock,
and recording/playback is synced to this rather than the system clock.  You'd have
to account for drift between the two.  (Though I did see a reference somewhere that
pro studio systems often have a means of using an external clock for sampling,
so I suppose this could be synced somehow.)

The Haiku OS that I'm most familiar with has an elaborate scheme for translating
between "Performance Time" (the sample clock) and "Real Time" (the system).
Buffers are passed around as events with a timestamp, so that should be translatable
to the common system time.  Don't know what other OSs do.

> Maybe for my use case there could be some kind of time code included in the resulting audio file so that individual files from different RPi:s could be merged into a synced multi-channel file?

This sounds like a good way.  Shouldn't be hard to devise a suitable format.
You might have to do some heavy interpolation in the post-processing if the
frame rates (from the original sample clocks) were too far off. 

	-- Pete --

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