I am looking for a story about a computer circuit that can write and synthesize music. Previously, people in the story had to create the instrumentation for electronic music by hand, even for electronic versions of classical music. This circuit was able to create an synthesized electronic version automatically, even vocal music. It was able to create very good performances of certain classical pieces, perhaps through the use of ultrasonic harmonics to make the music "feel" better. Then it was realized that the computer could also compose new music itself. So the person who made the circuit destroyed it because he thought it would eliminate all human usefulness.
That is Robert Silverberg's The Macauley Circuit, which first appeared in New Worlds #70 (April 1958).
The protagonist is awaiting trial and imprisonment as a "reactionary" for destroying the plans for the machine, and concludes his confession with "Gentlemen, we are all obsolete".