[PD] metro and drift

[Kyle Klipowicz]

This, my friends, is what the list is all about.

Good science guys!

~Kyle

On 4/1/06, Frank Barknecht <fbar at footils.org> wrote:
> Hallo Damian,
> Damian Stewart hat gesagt: // Damian Stewart wrote:
>
> > I set up three metros, one to bang once every beat, one to bang every
> > 27th of a beat (triplet-based time), and one to bang every 49th of a
> > beat (1/7th-based time). Then I left it running for a while, using timer
> > and realtime to measure drift over each beat. The patch I used is attached.
> >
> > Over 60 minutes:
> >
> > Between whole beat and beat counted from 27ths:
> > realtime 0.002ms drift
> > timer 0.144ms drift
> >
> > Between whole beat and beat counted from 49ths:
> > realtime 0.01ms drift
> > timer 0.149ms drift
> >
> > Between whole beat counted from 27ths and from 49ths:
> > realtime 0.002ms drift
> > timer 0.007ms drift
> >
> > Now, I'm not totally sure how to interpret these numbers, and certainly
> > don't understand the huge discrepancies between realtime and timer
> > outputs, but it seems like drift isn't going to be any problem for this
> > amount of time.
>
> You have a kind of bug in your patch because at several points the
> execution order isn't well defined. The [timer] output actually should
> not drift at all, as the clock used by timer to read the time is the
> same as the clock used by metro to "set the time", that is, its own
> period. The interesting number is the realtime measurement. Here also
> it is important to take care of execution order using [t b b] and such
> objects. Otherwise it will for example happen, that you get the time
> of different beat numbers.
>
> I attached a version of your patch that uses a well-defined execution
> order. The drift measuremeants are initiated by a delayed bang, so it
> will always measure the drift of the same beat.
>
> With that patch I get no time drift with [timer] as expected.  The
> results for the intervals between beats measured with [realtime]
> however ocillate regularily up to about 5 msec on my linux system for
> every metro period. As this happens in a very regular pattern I
> suppose this is some kind synchronisation problem between the Pd clock
> and the realtime clock of the operating system used in [realtime].
> Check the table "drift" to see the regularity of the pattern.
>
> Ciao
> --
>  Frank Barknecht                 _ ______footils.org_ __goto10.org__
>
>
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>
>
>


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