[LAU] transform midi Control Change 7 into velocity events?

[Dominic Sacré]

On Thursday 20 November 2008 23:49:46 Philippe Hezaine wrote:
> > I'm not sure mididings is the right tool for the job. The Python code
> > to transform the events would be quite simple, but mididings doesn't
> > support reading/writing MIDI files (yet?). You could of course use a
> > separate MIDI player/recorder, and route the events through mididings,
> > but you'd lose all meta information (tempo, time signature, etc.) from
> > the original file.
>
> Yes. I was sucessfull to loop a midi file with Jack and Rosegarden. The
> outputs was routed through mididings and went back to Rg for a new
> record on a new track. But it was not for this purpose and i didn't look
> for the meta information.
> But for now, if i have a copy about these informations may be i can try
> again this experience? It isn't a piece of music, only a succession of
> drums patterns. I can organize them to avoid different time signature...

Recording to a new track in the same Rosegarden session is actually a very 
good idea, I didn't think of that... You wouldn't lose anything that way.

As for the transformation, something like this should do the trick (not 
thoroughly tested):

from mididings import *

class Volume2Velocity:
    def __init__(self):
        self.vol = {}
    def __call__(self, ev):
        if ev.type_ == CTRL and ev.param == 7:
            self.vol[ev.channel] = ev.value
            return None
        elif ev.type_ == NOTEON and ev.channel in self.vol:
            ev.velocity = self.vol[ev.channel]
        return ev

run(Call(Volume2Velocity()))

> > As far as I can see, all tracks in your MIDI file are on the same
> > channel, so CC #7 messages on one track will affect the other tracks as
> > well. You should probably assign a different channel to each track.
>
> No. Like i have said these are drums patterns written by Lilypond. After
> the famous transformation i could join all the tracks in one if i want.

Yes, but then you need to do the transformation one track at a time. If you 
play multiple tracks through the same MIDI port on the same channel, some 
notes will get the wrong velocity (unless every note event is immediately 
preceded by a volume change).


Cheers,

Dominic