« Presenting Electric Gongs at Dorkbot 14: Thursday April 10th | Home | Electric Gongs update »

Photosequencer

I’m working on a sound-generating optical disc with multiple tracks of waveforms arranged in rings. The disc is mounted on a variable-speed motor (formerly a biological tissue homogenizer). Handheld LEDs shine light through the spinning disc and onto a light-sensitive pickup, and we hear its sound with guitar amplifier. Conceptually, I guess this related to the classic optigan keyboard and Raymond Scott’s esoteric circle machine.

The tracks on the disc play different pitched notes, arranged low to high from the inside track to the outside. I’ve made two discs so far. One has six tracks and plays notes from a scale in just intonation. The second disc, which is heard in this recording, has ten tracks, and plays the 8th thru 17th tones from the harmonic series. The ten pitches cover just over an octave; it is an 8-tone scale, but not equal tempered. Here are the pitches on the disc relative to the fundamental, which would be heard three octaves below the lowest pitch on the disc. If that makes any sense - it is overtone music.

• Track 1: 8th - three 8ves
• Track 2: 9th - three 8ves + maj 2nd
• Track 3: 10th - three 8ves + maj 3rd
• Track 4: 11th - three 8ves + flat dim 5th
• Track 5: 12th - three 8ves + perf 5th
• Track 6: 13th - three 8ves + sharp min 6th
• Track 7: 14th - three 8ves + flat min 7th
• Track 8: 15th - three 8ves + maj 7th
• Track 9: 16th - four 8ves
• Track 10: 17th - four 8ves + min 2nd

The disc is made of transparent material with black markings. If you shine light through it while it spins, the light intensity is modulated because the disc chops the beam. And if you shine flashing LEDs through it and catch the light with a pickup system, and it starts making music.

photosequencer

In this recording I’m playing the disc by holding a special LED flasher over the disc and moving it in patterns while aiming it at the pickup. The flasher has three LEDs that blink in synchronization at different frequency ratios. (Its actually part of an analog synth I’m building, but it turns out to be a nice source of blinking LEDs for this purpose!) Very small gestures control the polyrhythmic melody sequences. Its challenging to play, and I can see several ways to improve the flasher to make it more playable and expressive. I also need to find the cause of that obnoxious clicking sound.