Not-a-Theremin

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Not-a-Theremin Project

  • Owner: BuildBrighton
  • Start date: 03/10/2009
  • Completion date: 30/10/2009 ?

As a splinter group working on the [Theremin project] a few ideas have also been kicked around, which could result in an instrument that looks and plays like a theremin, but isn't really a theremin.

A few group members have already worked on MIDI projects and have discussed the idea of building a theremin-type machine with midi output. The analogue signal used to drive the oscillator/speaker on the original could be sampled to give a digital value within a specific range, which in turn can be used to generate a midi "note on/off" signal. The idea of using ultrasonic range finders in place of the theremin's antenna has also been thrown around. This would mean that the end result would be an instrument that plays like a theremin (non-contact) but is actually a completely different beast altogether.

Opinion is split as to which is the easiest/quickest to get working, and with October 30th deadline being the most important part of the project to meet, work on the two complimentary projects is ongoing in parallel.

How Not-a-Theremin could work

Ultrasonic sensors are used to return a distance value, from the sensor to the player's hand. This value is converted by an Arduino or other microcontroller into a MIDI key value and is output at the correct baud rate (31,250 bps) onto a serial pin. Since MIDI needs a signal to turn off a key pitch as well as a signal to turn it on, it is recommended that when the note changes, two MIDI signals are sent - one to turn off the previous note and one to activate the required note. It may be possible to program some sort of delay/sustain effect in here, so that the off signal is delayed. This would mean that note changes are not too abrupt as there could be a slight overlap between notes.

Volume can be controlled using a similar approach, using an ultrasonic transducer (or transmit/receive pair) that is away from the note-generating sensor (to avoid cross-talk or interference). Alternatively, a potentiometer, slider or rotary encoder could be used to control volume.

Additionally, optional "effects pedals" could be introduced - time permitting - to alter the MIDI output: instead of a single note, a chord could be played (a major or minor triad) by pressing a foot-switch or rocker pedal. Stress sensors or rotary encoders could be used to implement pitch bending. These are outside the original remit, and unlikely to be ready in time for the impending Oct 30th deadline, but offer food for thought for future development.


Links to source materials/ideas