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

  • From: Chris Grigg <gmpi-public@xxxxxxxxxxxxxx>
  • To: gmpi@xxxxxxxxxxxxx
  • Date: Fri, 13 Feb 2004 17:15:03 -0800

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.

Each processing frame is given as a fixed size, in samples.  We're
saying that events for a frame are passed in just before the frame is to
be processed,  In other words, conceptually the plugin gets 2 delivery
"packets" in every "duty cycle": events, then audio buffers.

Events are stipulated to be live within the audio frame.  We talked
about disallowing events to be delivered for future times.

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

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.

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?

Isn't it way, way more likely that audio buffers sizes will be constant in terms of number of sample frames, not constant in terms of musical time?

-- Chris G.

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