Urs also made a very clear presentation of previous version V1.0 of this MIDI feature on his website: http://www.gaudi.ch/OpenTheremin/index.php?option=com_content&view=article&id=200&Itemid=121, many thanks ! Since then, the software has been enhanced to V2.0 but there is still good applicable tips for the installation.
### Open Source Theremin based on the Arduino Platform
Open.Theremin is an arduino shield to build the legendary music instrument invented by Leon Theremin back in 1920. The theremin is played with two antennas, one to control the pitch and one for volume. The electronic shield with two ports to connect those antennas comprises two heterodyne oscillators to measure the distance of the hand to the antenna when playing the instrument. The resulting signal is fed into the arduino. After linearization and filtering the arduino generates the instruments sound that is then played through a high quality digital analog audio converter on the board. The characteristics of the sound can be determined by a wave table on the arduino.
For more info on the open source project and on availability of ready made shield see:
3. In "Application.cpp", take care of selecting MIDI mode that correponds to your cituation (put "//" in front off inadequate line - MIDI through serial is selected by default here):
//Serial.begin(31250); // Baudrate for real midi. Use din connection https://www.arduino.cc/en/Tutorial/Midi or HIDUINO https://github.com/ddiakopoulos/hiduino
The MIDI open theremin generates NOTE ON/OFF messages and Continuous Controler changes (MIDI CC) depending on settings and hands positions next to antennas.
In MIDI standard NOTE ON/OFF messages have a NOTE NUMBER and a VELOCITY.
Let's consider a Fade-in / Picth Variation / Fade-out sequence (I use right handed convention):
1. Fade-In
When left hand moves away from VOLUME ANTENNA (LOOP) and volume crosses a settable threshold (Volume trigger), a NOTE ON is generated. VELOCITY depends on how fast left hand is moving. Right hand position next to PITCH ANTENNA (ROD) determines the starting NOTE NUMBER.
2. Pitch variation
When right hand move next to PITCH ANTENNA (ROD), PITCH BEND messages are generated (if activated) to reach exact pitch as long as pitch bend range will do. Beyond, a new NOTE ON followed by a NOTE OFF for the previous note are generated if legato mode activated. Pitch bend range can be configured (1, 2, 7, 12 or 24 semitones) to align with synth's maximum capabilities.
3. Fade-Out
When left hand moves close to VOLUME ANTENNA (LOOP) and volume goes under Volume trigger threshold, a NOTE OFF is generated to mute the playing note.
The picture at https://github.com/MrDham/OpenTheremin_V3_with_MIDI/blob/master/MIDI%20Open%20Theremin%20V3%20HMI.bmp gives an example of possible HMI: on "Value" pot, red lines have 4 positions, grey lines have 5 positions and yellow lines have 8 positions. On "Parameter" pot you see coloured lines indicating which colour to follow for the "Value" pot.
Manipulation of "Rod antenna MIDI CC" and "Loop antenna MIDI CC" is not error proof. MIDI newbies should be advised to change their value in MUTE mode.
Audio processing from antennas to output jack, including volume and pitch pots, LEDs and button functions, is exactly the same as in open theremin V3. You can play the Audio and the MIDI side by side.
When legato mode is activated, if you trigger a note (with volume loop) and go in one direction (with pitch antenna) a new note will be triggered at the limit of pitch bend range.
Legato mode is used as a workaround for a limitation of MIDI (max 24 semitones pitch bend). Maybe some synth can perform pitch bend on more that 2 octaves but none of mine does...
"#define PLAYER_ACCURACY 0.2" -> Pitch accuracy of player. Tolerance on note center for changing notes when playing legato. From 0 (very accurate players) to 0.5 (may generate note toggling).
