PDP-8/M Plays Popcorn - Gershon Kingsley (Hot Butter version)

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.