Xint = Xint Is Not a Theremin
"In 1920 the Russian physicist Leon Theremin demonstrated the musical instrument that has since become known simply as the Theremin. Theremin died in November 1993, but his instrument lives on, occasionally being performed in concerts or used in soundtracks. The Theremin is unique in that it is played without there being any physical contact whatsoever between the performer and the instrument. The pitch of the instrument is controlled by the proximity of the player's hand to an antenna (mounted vertically in the original design). A second antenna (traditionally mounted horizontally) senses the proximity of the player's other hand and controls the volume of the tone. The experience of playing the device is far removed from that of performing music using a 'traditional' instrument. There is a perpetual feedback mechanism associated with the playing of the Theremin.
The feedback loop begins with the position of the player's hands, and next involves the sound produced, until finally the player processes what he/she hears and changes the position of his/her hands accordingly. A successful playing style requires the ability that a given pitch and volume of tone can be accurately converged on, and held by the player. Thus a competent Thereminist must have a good 'ear for music' and also good reflex action. Expert Theremin players have been few and far between with only a few names reflected upon when the instrument is mentioned."
from http://www.physics.gla.ac.uk/~kskeldon/PubSci/exhibits/E9/
build a digital theremin
| Part | Quantity |
|---|---|
| 4098 | 2 |
| TLE2027 | 3 |
| VCO8088 | 1 |
| VCA(SSM-2018) | 1 |
| LM759 | 1 |
| A/D Converter | 1 |
| D/A Converter | 1 |
| Z80 | 1 |
see schematic for more details (schematic from http://www.physics.gla.ac.uk/~kskeldon/PubSci/exhibits/E9/).
The digital theremin uses CMOS oscillators and logic gates to produce two DC levels. One DC level varies with the proximity of the player's hands from the pitch antenna, and the other DC level varies when the volume antenna is approached. The Z80 will be integrated into the digital theremin so that it can record and playback a short sequence of music. After converting the analog sound into a digital signal using an ADC, the Z80 will store these samples in memory to be played later when prompted. To make the digital theremin easier to play than its analogue counterpart, it will optionally implement "air frets." The Xint will discretize the pitch input into individual note values. This means that when the thereminist's hand is within a certain range, the instrument will produce, say, a middle 'C' rather than requiring that their hand be exactly at the position that would produce this pitch. In addition to making the instrument easier to play, this greatly simplifies the task of recording a sequence of music for later playback. rather than storing data continuously, a few bytes per sample point (which, with a suitably high sample frequency, would eat up memory quickly), we can simply use run-length encoding to specify which note to play and how long to hold it. Another task of the Z80 will be to manipulate the sound to produce distored music. Other features may be added at a later date.
