[gmpi] Re: Topic 6: Time representation
- From: "Michael Gogins" <gogins@xxxxxxxxxxxx>
- To: <gmpi@xxxxxxxxxxxxx>
- Date: Wed, 30 Apr 2003 21:15:15 -0400
All of these problems (what is the modulus of time?) are obviated by having
time as absolute seconds from start of performance, double-precision
floating-point. There are no particular performance problems with that. If
there is a problem with rounding errors in converting to/from musical units,
then absolute sample frame from start of performance should be used.
For musical time, bar/beat/tick makes sense. What about also having first
and second derivatives of tempo? (by tick).
The host should also maintain, in an efficiently queried format, such
quantities as seconds per sample frame, seconds per tick, and so on.
===========================================
Michael Gogins
gogins at pipeline period com
Irreducible Productions
Silence, a language for programming music and sound
Available at http://www.csounds.com
===========================================
----- Original Message -----
From: "Mike Berry" <mberry@xxxxxxxxx>
To: <gmpi@xxxxxxxxxxxxx>
Sent: Wednesday, April 30, 2003 4:14 PM
Subject: [gmpi] Re: Topic 6: Time representation
> Samples/sec is simply not accurate enough. I know this sounds strange
> in an audio plugin API, but I want to be able as a host writer to set
> the time representation that I think is necessary for my app. In the
> case of a video editor, I need a tick resolution whihc is lined up with
> my video rate AND my audio rate.
>
> So I consider it a necessity that the host be able to specify the ticks
> per second. Some hosts might use a sampel rate for this. But not all.
>
> Tim Hockin wrote:
> >> Please do not specify that the clock is in the audio sample rate. Leave
> >>it up to the host to specify to the plugin what the ticks per second is.
> >>This value would be retrieved by the plugin at startup, and would be
> >>guaranteed never to change during runtime. The plugin would then be in
> >>charge of turning ticks in the host's resolution into samples or beats
> >>or whatever they needed internally.
> >
> >
> > If ticks is always related to samples by a constant factor, and
everything
> > must convert between the two ehy not just represent timestamps as
samples
> > and be done with it.
> >
> > In my discussion, I always meant ticks in relation to musical time,
which is
> > to say - NOT related to sample time in any direct way.
> >
> > I think we all agree that some constant, monotonic, absolute value is
the
> > fundamental timestamp. Samples are used everywhere, and the host
already
> > provides knowledge of samples/sec.
> >
> > More from me as I work through the list of messages to which I must
respond.
> >
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> >
>
>
> --
> Mike Berry
> Adobe Systems
>
>
> ----------------------------------------------------------------------
> Generalized Music Plugin Interface (GMPI) public discussion list
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