Fictional electronic keyboard synthesizer, from Lloyd Biggle Jr.'s short story "The Tunesmith." It first appeared in Worlds of If magazine, August 1957. Biggle actually had a PhD in musicology! Multichords have an automatic setting that lets it "practically play itself." Tone quality is changed by flipping on "filters."
In the story, composer Erlin Baque is forced to turn to playing one live in a restaurant after the ad jingles ("Coms") he composes don't pay the bills. The story is set in a future where, like the 1993 film Demolition Man, ad jingles are the ONLY music people listen to.
Baque did not answer. He was examining the multichord. It was a battered old instrument, and it bore the marks of more than one brawl. He fingered the filter buttons, and swore softly to himself. Most of them were broken. Only the flute and violin filters clicked into place properly. So he would have to spend twelve hours a day with the twanging tones of an unfiltered multichord.