Thanks to the guys of Montreal Electronic Music for this tip. An old PDP computer playing Kingsley’s Popcorn.
The explaining text says: “A popular tune written by Gershon Kingsley and popularized by Hot Butter, played on a period-correct 1970s minicomputer! With a new (and very simple) audio interface from the PDP-8/M’s Omnibus connected to a Cordovox amplifier cabinet, sound quality is much improved over previous AM radio experiments. This computer boots OS/8 off of a Raspberry Pi running SerialDisk, using a laptop as a serial terminal. MUSIC.PA was written in the 1970s and supports four notes of polyphony, which is usually sufficient for making recognizable music. The oscilloscope is sampling the output of the audio interface (a 74123 retriggerable monostable multivibrator tuned to 7 microseconds triggering on the INITIALIZE signal), showing that the audio output consists solely of pulses. The program uses a series of pulses to increase the volume, and uses more pulses for lower frequencies to better equalize the sound.”
If I remember well MUSIC.PA was written in Fortran. Very nostalgic and a nice tune. Although a mobile phone these days will do it better: with 128 notes polyphony, graphic DAW, and complete synthesizers …
We found this video about a PDP/1 playing music. We certainly must do a feature on these first computer operated sound machines (…soon!)