hi,
I have experimented with sync-ing generative computer apps in a number of ways.
Never did a proper experiment so was just to ear responses.
Found the timestamped udp network to be a real problem
The audio sync was real good in terms of stop/start and progression
through score.
However another approach that I tried was using NTP. If the laptops
were allowed to run for a bit and settle there system clocks I found
that it was possible to queue events against the system times.
In direct response to your question I find the motu drivers tend to be
latency stable once running so there tends not to be jitter with the
latency time.
Scott
On Thu, Dec 17, 2009 at 4:28 AM, Andrew Sorensen <andrew_at_moso.com.au> wrote:
> OK, so hopefully all of this is going to make some sense :)
>
> I've been building some more advanced sync/clock related stuff into
> Impromptu recently and am getting some pretty good results. My question to
> the list is that I'm looking for ideas about the most accurate way to test
> the sync without resorting to specialist hardware (GPS clocks, network cards
> with timestamping etc.).
>
> At the moment my testing approach is to schedule regular pulses from up to 8
> host machines running Impromptu and record one output channel of each into
> another machine with an 828. I can then measure the difference between the
> pulse times in samples between the (up to 8) recorded audio channels. This
> seems a pretty accurate test and I'm getting a reliable sync and my early
> experiments indicate an offset range between 1 and 5 samples (< 100
> microseconds at 44.1k).
>
> The sync results (i.e. the measured clock times of the hosts involved) as
> reported by the "impromptu time server" confirms my audio results but
> paranoia of the unknown remains strong :)
>
> My paranoia is that there are going to be buffering issues with the
> hardware/device drivers as well as delay on the wire etc.. I don't have
> much experience with these issues. How much variation should I expect
> between each hosts audio data leaving its DAC and being successfully
> processed (i.e. both ADC and Device Driver latency) via the 828. How much
> should I be worried about the latency of the audio signal from the time it's
> sent from each host to the time it's received. It's not the overall but the
> relative delays I'm primarily concerned about. Are we talking nanoseconds
> or microseconds of difference between each sending host here?
>
> My assumption with all of this is that I'm going to get better accuracy
> (with less precision) from an audio signal than sending time-stamped UDP
> over a gigabit LAN?
>
> If anyone has any thoughts on the accuracy of my tests and what I might do
> differently to improve upon them (without resorting to specialist hardware)
> I'd love to hear them. I'm running OSX but thoughts relating to any
> OS/audio hardware welcome.
>
> Cheers,
> Andrew.
>
Received on Thu Dec 17 2009 - 23:47:55 GMT