[gmpi] Parameters / controls / GMPI event system - refreshment

  • From: "Koen Tanghe" <koen@xxxxxxxxxxxxxxxxxxx>
  • To: <gmpi@xxxxxxxxxxxxx>
  • Date: Thu, 24 Nov 2005 16:53:17 +0100


I'm currently starting to set up some abstract class for a "music-processing
block" for my own internal purposes and I was re-reading the GMPI spec so as
to make sure my stuff will be easily adaptable to the GMPI system when it's

Now, I was wondering if someone could refresh the reasoning behind the
following GMPI concepts: parameters, controls and GMPI events (all of them
are different terms coined in the first final draft proposal:
http://www.gmpi-plugins.org/ ).

In section 1.3 we talk about "audio" and "controls" as possible types of
inputs and outputs.
Then, in section 3.8 we talk about GMPI "events", but only in terms of
"event delivery to a plugin", no event delivery *out* of a plugin.
Then, in section 3.11 we talk about "parameters" and say that plugins expose
their parameters to the host and that parameters are automatable (thus
directly modifiable by the host).
Finally, in section 3.12, we briefly talk about "control" input AND output.

Now, do I remember correctly that:
- GMPI events and controls are one and the same?
- parameters can only be changed through GMPI events/controls?
So, essentially, that:
- a GMPI plugin can only have two types of inputs and outputs: audio and
events (= controls)?
- parameter changes (either incoming or outgoing) all come through GMPI
events (= controls)?
This means that all of the following semantic things:
a. "start audio sample generation for a new C4 note"
b. "signal a snare drum event detection at time offset xyz"
c. "change the cutoff frequency of the filter to 200 Hz"
must come in to (a and c), respectively out off (b) the plugin using GMPI
events through a control port (aarghh, another term...)?
Or can a parameter change be done without going through a control port using
GMI events?

audio   --->+  GMPI     +-----> audio
           !  plugin   !
control --->+           +-----> control

And parameters don't come into this picture (except indirectly through the
control ports?

Just need some reassurance here, and it might also keep us fresh ;-)


There's also the "clock/time related" input and output, but this will probably be handled through special controller messages, but I could be wrong, and for this post it doesn't matter really...

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