[sdiy] MIDI CC with Pots

Jacob Watters jacobwatters at gmail.com
Sat Oct 4 07:01:02 CEST 2014

I had a discussion with a friend about a synth that he is working on.
We disagreed about the proper way to handle MIDI CC. Normally, I would
tell him to do it the way the works best for him, but he intends on
selling the synth. Since that is the case, then I think that it needs
to work in a way that musicians expect it to work and that it should
not place unnecessary limits on its usage. Please let me know your
thought on how to handle the following two situations.

-= PROBLEM 1: MIDI CC and Pots =-

The synth has several pots for adjusting various controls of the sound
(knob per function). The controls will also respond to MIDI CC. There
can be a conflict in how the synth responds to both messages.

OPTION 1: I recommended having the synth use whatever message it last
received, whether a pot change or a CC message. This provides
flexibility in usage and allows the use of both MIDI CC and the pots
at the same time. This is how most of my synths seem to work.

OPTION 2: The flaw with the previous method is that if a CC message
turns a value all the way down, then when the pot is moved the value
will jump up to where the pot is positioned. Encoders or a "catch up"
or "pass through" method will add a bunch of extra code that will slow
everything down and limit the abilities of the synth. To him, the
sudden change from the MIDI CC value to the pot value is not
acceptable (even though I have synths that work this way). He wants to
put a switch on the synth to change from either MIDI CC or pots. The
synth will never be able to respond to both at the same time. This
limits it in that you can't adjust a pot by hand while a MIDI
sequencer changes other values automatically.

What option would you prefer? What other suggestions do you have that
haven't been mentioned?

-= PROBLEM 2: Mod Wheel =-

First, he had a control that could only be changed by the mod wheel.
The synth has no built-in mod wheel (MIDI control only) so I explained
how some synths have a joystick style pitch/mod control. On these
synths, the mod level is always reset to 0, so it would not be a good
idea to use it as a dedicate control. He agreed to add a dedicated pot
to the synth for that control. However, there is still some
disagreement about how the MIDI modulation messages should be handled.

OPTION 1: I pointed out that the mod wheel is usually used for
modulating an existing control that has its own value already. It adds
more LFO to the oscillators or opens the filter more than the current
cutoff setting. It is not usually a dedicated control on its own. This
means that it only adds to the current value of a control that is set
with a pot on the synth. Since he agreed to add an extra pot for the
thing that the mod wheel will control, this is very easy to employ and
won't slow the synth down much (just add the mod CC to the current pot
value and limit it to the max value of the control). This also means
the pot for the control will have its own dedicated CC for setting the
base level, and the mod CC will only add to that.

OPTION 2: He wants to add a switch to change the way that the synth
handles the mod CC. This will allow the control to be disabled for
anyone who is using a joystick style pitch/mod controller. This limits
the usage of the synth for some people (anyone using it with a

OPTION 3: He also talked about the possibility of not using the
modulation CC at all. I own many synths, and all of them that have
MIDI respond to the mod wheel CC. I think that this would be a bad
idea because musicians expect the mod wheel to do something.

Again - what option would you prefer? What other suggestions do you
have that haven't been mentioned?

Thanks for your help resolving this debate!

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