[PD] logical timing question

Roman Haefeli reduzierer at yahoo.de
Sun Jan 11 15:48:49 CET 2009

On Sun, 2009-01-11 at 13:42 +0100, Peter Plessas wrote:

> I did this test with -audiobuf 50 running OSS.
> You are right, the values differ greatly on the kind of audio driver i 
> am using, f.e. with alsa and -audiobuf 50 i get:
> print: 0.1
> print: 4.928
> print: 4.991
> print: 4.951
> print: 4.994
> print: 0.098
> print: 4.931
> print: 4.994
> print: 4.949


> So realtime is dependent on the audio clock? I always thought that it 
> took the cputime/OS time...

i still think, that [realtime] is _not_ dependent on the audio clock
(without having read the code). the issue here is the moment, at which
the time from OS clock is polled. from what i understand, the pd process
is driven by the audio driver, respectively by its clock, so the time,
when the 'bang' to [realtime] is executed, is dependent on the
implementation of the audio driver. even when not having drop-outs, you
wouldn't know exactly, when [realtime] polls the system clock. this
could be somewhere between now (0ms) and chosen latency. that is why you
get the jitter, when measuring with [realtime]. 

i once could make use of this two different time measurement methods to
tune the jack-server running with the dummy driver to the correct


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