page_title: Optigan
section_title: The optical disc format
hierarchical_section_title: Optigan / The optical disc format
caption_attribution_description: English: An Optigan Program Disc, containing the program "Sleigh Ride." The disc is made of clear flexible plastic with black grooves, and is 12" in diameter - the same size as an LP record.
context_page_description: The Optigan is an electronic keyboard instrument designed for the consumer market. The name stems from the instrument's reliance on pre-recorded optical soundtracks to reproduce sound. Later versions were sold under the name Orchestron.
context_section_description: The Optigan's playback system functioned much like the storage and reading of an optical soundtrack as was used in motion pictures, using a light bulb to energize a row of photodiodes on the opposite side of spinning, 12" diameter clear plastic film discs (officially referred to as "Program Discs") encoded with fifty-seven concentric optical tracks. The system then translated the analog waveforms on the disc to an audio signal.  A flip-down door beneath the keyboard allowed access to the disc's loading area to the left of the unit and a disc storage area to the right. Program discs were loaded by simply sliding them onto the felt-covered platform; a V-shaped notch on the front of the panel aided in alignment.  When power was applied and the front cover closed, a spindle engaged the center hole of the disc and a motor-driven idler wheel spun the disc on the spindle.  The power switch itself was mechanically linked to the disc's drive system; lowering the front panel dropped the spindle and disconnected power to the instrument, allowing the program discs to be changed without the need to fully power down.  A broad, flat, white plastic cleaning tool with a purple, simulated velvet cleaning surface was supplied with each Optigan to allow periodic cleaning of the photoelectric cell, located near the rear of the instrument.
  Thirty-seven tracks were sustained or repeatedly percussive notes in the timbre of a particular instrument and were played through a standard three-octave piano-style keyboard with the right hand; twenty-one were of a live band or soloist playing chords in different keys arranged per the circle of fifths, specifically B-flat, F, C, G, D, A and E major, minor, and diminished and were played with the left hand in much the style of a chord organ or accordion. The remaining five were assigned to rocker switches above the chord buttons and featured (depending on the disc in question) percussion, sound effects, introductions, vamps, and endings synchronized with the chord buttons.  Pushing upward on the rocker switches locked them in place for use with percussion; pushing downward allowed momentary use for vamps, introductions and endings.
  Not all of the chord buttons had their own track assignments, the result being only fifty-seven sounds on sixty-three buttons, keys and switches. There was also an optical metronome incorporated into the discs which showed as a red flashing light for the downbeat and white for the upbeats inside the Optigan badge above the keyboard. The advantages of this unique optical playback system were that the Optigan's range of timbres was infinitely expandable and that there was no limit on the duration of a note as there was on the Optigan's professional-grade counterpart, the magnetic tape-based Chamberlin or its successor the Mellotron. The disadvantage was that notes could have neither attack nor decay, as the tracks had no specific beginning or end.
  The "Starter Set" sold with the Optigan contained discs with fairly self-explanatory titles:  "Big Organ & Drums", "Pop Piano Plus Guitar", "Latin Fever", and "Guitar in 3/4 Time".  More modern styles were represented by titles such as "Movin'!", which was a rhythm and blues disc and "Hear and Now", with a sound clearly based on the hit single "Sweet Seasons" by Carole King (and cover art evocative of that of her Tapestry (1971) album). Other discs were marketed individually and packaged much like long-playing phonograph records. These individual titles were also bundled in much the same way as the "Starter Set" and sold as six-disc "Entertainment Folios".  Some discs were available only as part of a two-disc "Style Pak" with titles such as "The Joyous Sounds of Christmas", "Country Style Pak.", "Polka" and "Songs of Praise" - these last two being produced towards the end of production and in very low quantities. Music books of various styles and even arrangements intended for individual disks were also available and sometimes packaged with the different bundles.
  The initial run of musical tracks were recorded by Southern California stu
caption: An Optigan Program Disc
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