[sdiy] MIDI volume to volts formula

Gordonjcp gordonjcp at gjcp.net
Wed Jun 6 09:07:59 CEST 2018

On Tue, Jun 05, 2018 at 11:24:21PM -0700, rsdio at audiobanshee.com wrote:

> All we can say for certain is that larger Velocity numbers must be louder, but only if velocity is applied to volume.

Unless you're doing something a bit off-the-wall ;-)  Negative velocity
values can be handy if you want to layer two sounds and crossfade
between them.

> Personally, I always try to consider the techniques available at the time. You have to keep in mind that bother the sender and the receiver could interpret velocity any way that they wanted. Usually, especially in the eighties, manufacturers wanted to find the easiest way to calculate these values.

The Ensoniq Mirage maps velocity to attack peak level and sustain level
by applying a proportion of incoming velocity converted to a signed
value, and looking up an exponential-ish table in ROM.  I haven't got
the right bit of source code kicking around to look at so I might not
be remembering it properly.

Since as you say the early 80s 6809 processor couldn't divide (but could
multiply) then a lot of that stuff was just done by lookup tables.
Never underestimate the power of throwing inexpensive memory at an
expensive calculation.


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