[gmpi] Re: 3.15 MIDI
- From: "gogins@xxxxxxxxxxxx" <gogins@xxxxxxxxxxxx>
- To: gmpi@xxxxxxxxxxxxx
- Date: Fri, 18 Jun 2004 14:16:25 -0400
This is a good point to raise.
I suggest again two modes, "compatibility mode" in which it's arbitrary what
the mappings are is it currently is in MIDI, and "extended mode" in which
there are either (a) predefined mappings for common musical semantics, or
else (b) the plugin can register an opcode and a mapping as we discussed
previously.
----- Original Message -----
From: "Chris Grigg" <gmpi-public@xxxxxxxxxxxxxx>
To: <gmpi@xxxxxxxxxxxxx>
Sent: Wednesday, June 16, 2004 10:59 PM
Subject: [gmpi] Re: 3.15 MIDI
> Jeff said:
> >Ron said:
> >> I'm not convinced this is achievable. For example, let's consider the
> >> conversion of MIDI volume controller to GMPI. MIDI volume doesn't
have a
> >> standard mapping from 0-127 to gain values. So how does this value
get
> >> converted within GMPI? How the does the converted value survive the
round
> >> trip through a processor that does:
> >> MIDI -> GMPI - > [Event Processing] -> GMPI -> MIDI.
> >
> >All 7 bit controllers get converted like so....
> >
> >float gmpi_value = (float) midi_cc / 127.0;
> >
> >.. and converted back like so...
> >
> >int midi_cc = (int) (gmpi_value * 127.0 + 0.5);
> >
> >( as usual, i've probley made some terrible coding error, like forgot a
> >semicolon, or rounded down instead of up, but I hope you get the gist)
> >
> >Don't assume the conversion to GMPI is some over-complicated thing,
we're
> >not going to convert everything to Angstroms or anything. It's just a
> >converion to floating point.
> >
> >The intention isn't to reinvent the whole thing, only to give controllers
> >more resolution by converting to floating point.
>
> I think what Ron meant is, out of 0-127 MIDI CC values, where's the
> nominal 0 dB point? What midiVolNumber-to-dB-curve is used? MIDI
> per se doesn't specify either thing, whereas we said GMPI parameters
> would use natural/perceptual units, so for volume presumably that
> would be expressed as dB. There is no MIDI-spec-governed conversion
> between the input and the output, so each plug can decide to do a
> significantly different thing, so in fact the host doesn't have
> enough information to make the conversion, contradicting your claim
> that the conversion is always trivial. You can see the problem.
>
> -- Chris G.
>
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