[gmpi] Re: Reqs 3.9. Time - opening arguments.1

  • From: Tim Hockin <thockin@xxxxxxxxxx>
  • To: gmpi@xxxxxxxxxxxxx
  • Date: Wed, 11 Feb 2004 13:19:15 -0800

On Wed, Feb 11, 2004 at 12:16:44PM -0500, Ron Kuper wrote:
> >>>
> Personally, I would prefer to see tempo specified as a list of
> timestamped "tempo events" for that buffer (the way MIDI events are in
> dealt with in VST). The plugin can then perform sample accurate event
> handling for that buffer.
> <<<
> I don't think tempos can be events.  Here's why I believe this, please
> explain why I'm off base about this.

It's a real issue in concept, but I think it can be constrained..

> Let's say for arguments sake our audio frame size is equal to 1 beat =
> 960 ticks (assuming MIDI parlance for a second) at whatever the current
> tempo is.  Every set of events that are passed in live within the next
> beat, and can be safely rendered in the next beat-sized frame.
> Now I allow a tempo event to come in.  This event slows the tempo down,
> so that one audio frame is now equal in duration to 1/2 a beat or 480
> ticks.  
> If the host is feeding these events to the plugin, the host now needs to
> be careful about what events get sent after the tempo change, to ensure
> that we don't send more events than fit in a single frame.

Right, the host needs to be aware of tempo changes, as does anything which
uses musical timing internally.  If you think of the host's
sequencer/automation engine as plugins (whether they are or not..) and
tempo-masters as plugins, then it's a matter of dependencies.

The sequencer plugins depend on the tempo plugin.  In a graph, that means
the tempo plugin must be processed BEFORE anything that cares about tempo.

> If a plugin is sending these events to other plugins, how do the other
> events in the other plugins "know" that they are now out of range for
> the audio frame?

So if your plugin cares about tempo, you will be notified of a tempo change
BEFORE you send any events.  When you see a tempo change, you know to not
send events that would be out of range.

If your plugin does not care about tempo, but sends events, then it must be
presumed to want sample-based timing and not musical-based timing.

Does that answer that?

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