Powered by Squarespace
« Simulated surround sound with Waves Nx | Main | Florida Keys »

Radial Motor Faders

Last year, when I took Sound in Media (a history of film class focusing on sound) we watched a fascinating BBC documentary on the BBC Radiophonic Workshop: http://youtu.be/DFznOcOOSec
(worth a watch)

While watching it I noticed something I hadn't seen before.  A fader of sorts, but instead of your typical rotary or linear fader, it was a radial fader.

(a still image from the doc)

Here it is queued up in the video (watch closely, it's very brief):

If I had to guess, it's essentially a regular rotary fader connected to a perpendicular shaft, allowing you to move the fader along an arcing path.  That gave me an idea, what if you could make a Radial Motor Fader?

You could use a servo instead of your typical linear motor fader, since a servo is essentially a motor with a potentiometer in it for positional data (exactly the same as a motor fader).  However the problem is that most servos don't allow you access the potentiometer.  I posted on an electronics forum with this idea, but didn't really get any responses (should have posted on an audio forum...).

I had pretty much shelved the idea until I was browsing Adafruit today, and saw this:


A custom made servo with the feedback (potentiometer) line brought out.  This is exactly what I need to create some radial motor faders, (and at $15 it's a bit cheaper than linear motor faders, ~$20).

I've already done some research into emulating motor faders with Pro Tools, from my Pro Tools Additive Synthesizer.  MotorMix will probably be the best protocol to use, since the developer freely posts their protocol.  The Mackie HUI protocol has been reverse engineered on several occasions, but it's copyrighted.  Avid ICON and EUCON protocols are completely locked down, and not worth the trouble (which is too bad, since they support more that 8 faders at a time).

Basic microcontroller work flow:


  1. Receive MIDI data.
  2. Set fader positions.
  3. If knob is touched, deactivate servo, read analog values, and send MIDI data.


The MotorMix protocol works essentially like this:


  1. Touch fader, send midi note on.
  2. Value set by pitch bend CC from midi channels 1-8.
  3. Release fader, send midi note off.
  4. Fader positions receive via pitch bend CCs.


PrintView Printer Friendly Version

EmailEmail Article to Friend

References (1)

References allow you to track sources for this article, as well as articles that were written in response to this article.
  • Response
    Response: drones
    These are the ideas for the faders through which the ... have become more acceptable in the market for the commercial use because these also require to fulfill the requirements of the international standards.

Reader Comments

There are no comments for this journal entry. To create a new comment, use the form below.

PostPost a New Comment

Enter your information below to add a new comment.

My response is on my own website »
Author Email (optional):
Author URL (optional):
Some HTML allowed: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <code> <em> <i> <strike> <strong>