Change velocity while MIDI note is playing

[zorglub76]

Hi guys,

I'm trying to make a midi controller that would take piezzo sensor as an input and output a midi message.
This means that I would like the following behavior:

 - Piezzo is hit, it sends a Note On message
 - After being hit, piezzo changes voltage in analog manner - I want the velocity of my MIDI note to change in accordance.
 - Piezzo's voltage is below threshold - Note Off is sent.


I cannot find an example where velocity would be changed while MIDI note is on.
Anyone knows how to handle this?

[PieterP]

What you want is 'aftertouch'. You need to send Polyphonic Key Pressure events.

You can find more information in the MIDI specs, it's the same principle as note on/off events, just the first nibble is different.

Pieter

[zorglub76]

Ah, great! Thanks!
Didn't know what that was called..

[Grumpy_Mike]

Note that all MIDI sound generators do not respond to after touch and many of those that do only apply one value to all playing notes. A very few apply it separately to each individual note.

[zorglub76]

Hmm.. yes, now, when I think of it, I might throw away the idea of aftertouch.

I want to make a foot controller - you stomp on it and you get some kind of a drum sound (e.g. you play guitar, and stomp to get hihat, or cajon, or tambourine, or something similar to accompany your playing).

I wanted it to be able to play both sampled instruments and synthesized ones. And so I thought that I would need aftertouch to shape the sound. But now I realized that both samples and synthesizers do "attack/decay/sustain/release" thingy, and I have absolutely no need for aftertouch...

Damn.. Now it looks simple..