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Re: [fluid-dev] New patch: polyphonic key pressure (aftertouch)

From: Kjetil Matheussen
Subject: Re: [fluid-dev] New patch: polyphonic key pressure (aftertouch)
Date: Tue, 23 May 2017 14:43:56 +0200

On Tue, May 23, 2017 at 2:33 PM, Marcus Weseloh <address@hidden> wrote:

2017-05-23 14:00 GMT+02:00 Kjetil Matheussen <address@hidden>:
So when fluidsynth receives these bytes:

0xa0 0x60 0x10
0x90 0x60 0x70

Is the note played with a volume value of 0x10?

That depends on the modulators on the instrument. Polyphonic aftertouch is not one of the standard modulators, so it needs to be explicitly added to an instrument / preset. On the standard FluidR3_GM font, your example would play with volume of 0x70, as there is no polyphonic aftertouch modulator on any of the presets.

If you add a Key Pressure -> Initial Attenuation modulator and leave the default Velocity -> Initial Attenuation modulator in place, then those two modulators will work in combination. So in that case: yes, sending aftertouch before note on will affect the initial volume of the sound. But it probably wouldn't be 0x10 in your example, because the velocity also adds to the volume through the default modulator.

By the way, that is (as far as I can tell) exactly the same behaviour as in the already implemented Channel Aftertouch event. Channel aftertouch is always accepted and stored on the channel, even if no note is currently playing and it is also not reset on note off. But Channel Pressure / Aftertouch _is_ one of the default modulators and is mapped to LFO Pitch Depth. So if we switch your example to Channel Pressure:

   Channel Pressure: 127
   Note On: 60 127

then that note starts with maximum volume and maximum LFO pitch depth.
In case, that doesn't seem right...

Ok... but what _is_ right? :-) And if that's not right, is the existing channel pressure also wrong?

Thanks for the explanation! It seems seems like polyphonic aftertouch
is a more advanced feature than I though, and you know a lot more
about this than me. I thought polyphonic aftertouch was just a way to
change the individual volume of single notes after they have started

It would be very nice to have a simple option for setting the volume of individual
notes after they start playing though. But perhaps that would require a different
type of extension to fluidsynth?

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