On 21.12.15 03:48 , Bjorn Roche wrote:
> Generally speaking, a program like ProTools (the "host app") will open a
> plugin, and ask for a list of parameters. The plugin will respond with
> something like "These are my parameters and they have the following
> basic properties (id, display name, min, max, default values, etc)."
> Sometimes they supply more info like "this parameter has a unit of
> dB/Hz/Whatever and is measured on a log/linear scale". Theoretically,
> they supply enough info for the host app to build a UI without needing
> the plugin to do so, and well-built plugins do this.... but most
> commercial plugins aren't "well-built" in that sense.
If I recall correctly, for VST2 plugins the range is always 0..1 (or
something standard that the plugin cannot modify) and it's the plugins
job to scale the parameters correctly. Audio Unit plugins report things
like range, default value, and unit of measurement. I am told that VST3
supports plugin-defined ranges as well. I have no idea how it is with
AAX or other plugin formats.
>> second, specifically, how is this data defined in a MIDI file?
>> specifically which MIDI controls (the control numbers) are, by
>> default, assigned to parametric EQ? how many can a single MIDI
>> channel have?
>
>> and then how is the scaling defined? presumably 0x40 would
>> represent the middle of the knob range. where does that go for f0?
>> and for Q? i presume 0x40 would correspond to a dB gain of 0.
>
> I don't recall any MIDI standards about this. If there are any, I doubt
> anybody abides by them. That said, I'm not really up on all the areas
> where this would be relevant (e.g. midi controllers might have a use for
> this), so it's very possible that something exists.
There is the XG standard that defines a mapping for MIDI CC values to EQ
frequencies among other things. But I doubt that anybody who's goal is
something other than supporting XG sound generators will bother with
that. In the end it's all rather arbitrary.
Thomas
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