[ntp:questions] Can NTP sync within 1ms

Rob nomail at example.com
Sun Apr 27 10:43:02 UTC 2014


Paul <tik-tok at bodosom.net> wrote:
> I don't know what "terribly accurate" might be to you but in the real world
> sufficient accuracy depends on the circumstance.
>
> Someone should conduct an experiment.

I am in a group that works on a project that needs synchronous audio
on geographically distributed PCs.

Of course there are several hurdles.
First, we sync all machines to locally connected GPS receivers with
PPS output.  We use ntpd and kernel PPS.  This is wellknown territory.

In the ntpq -p stats this appears to bring the systems within 10us,
often within 2us, of the PPS signal.  We still have to find out if this
is reality or just output of a program.

The next problem is to send output to a soundcard and making it send
a sample at the sampling clock edge closest to a specified time.
(48kHz sampling rate corresponds to a sampling clock period of 20.8us)

When that has been achieved, it of course is easy to wire up two of
those systems, place them closely together, and check on a scope.

It could be further improved when we can somehow lock the sampling
clock to the PPS signal, so another +/- 10uS uncertainty/jitter is
removed.



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