[LAD] Open Keyboard: Request for velocity curve information

David Olofson david at olofson.net
Sun Oct 4 16:50:38 UTC 2009

söndag 04 oktober 2009 10:21:09 skrev  Albin Stigo:
> Hi,
> Many thanks for all feedback on my original posting about what
> features you would like to see in an open midi controller...
> Based on your "requests" I've started experimenting a bit with adding
> rotary encoders and a 20x4 lcd display. I've changed to a more
> powerful (but still cheap and easy to work with) microcontroller
> atmega128 (from atmega16). If you're not familiar with
> microcontrollers you might be familiar with the arduino platform which
> also uses an atmega (but the lesses atmega168).

I have a few Atmel MCUs lying around, actually... :-)
I should start playing around with them some time. Any year now... :-D

> Now to my question: Does anyone have some sample velocity curves, like
> a mapping from key velocity to midi velocity for different instruments
> (grand piano etc)? There doesn't seem to be any convention on how to
> handle velocity data??

Don't know... I would expect the velocity (as in m/s) to have a rather non-
linear relation to the MIDI velocity values. I mean, kinetic energy is 
velocity squared, so one would expect double actual speed (ie m/s) to add 12 
dB to the resulting output level, assuming the instrument response is linear.

But, I'm only guessing! I suspect it'll come down to trial and error, finding 
something that "feels good".

> Does some synths expect linear mapping and does the "mapping" in software??

Well, I don't know about linearity, or how linear MIDI velocity is actually 
supposed to be, but it's common to at least have various ways of scaling 
velocity. Many (most?) synths will support mapping of velocity per voice to 
create "analog" layers (crossfade rather than switch at a distinct velocity), 
and to exaggerate, reduce or disable velocity response and things like that.

I have a faint memory of the Roland JV-1080 having some sort of programmable 
exponential velocity mapping as well, but I could be wrong... Don't have mine 
here, so I can't check.

//David Olofson - Developer, Artist, Open Source Advocate

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