When Jimi Hendrix pushed a Marshall stack into self-oscillation on a Monday morning in August 1969, he converted an engineering defect into political speech. The anthem came apart under the feedback, and the coming apart was the point. Nobody in the field needed the liner notes.
What feedback actually is
Feedback is a loop that has stopped asking permission. The pickup hears the speaker, the speaker plays the pickup, and the system finds a frequency it likes and stays there, louder and louder, until someone moves. It is the only sound a rig makes on its own initiative. Engineers spend their careers preventing it. Musicians spent the second half of the twentieth century courting it.
The microtonal content of a feedback howl is not noise in the information-theory sense. It is extremely specific: a room, an amp, a pickup, a distance, and a body, all resolved into a single pitch that does not exist on the piano. Move six inches and it changes. That specificity is why feedback cannot be sampled honestly. A sampled howl is a recording of a decision. A live one is the decision.
Turn it up until it sings, then stand where it hurts. — Overheard soundcheck instruction, 1991
A short taxonomy of the scream
- The controlled bloom. Sustain that tips over into a harmonic. Rock’s basic vocabulary since 1965.
- The stand-off. Guitar held to the cabinet at a fixed angle; the player becomes a component. Whole careers have been built on the geometry.
- The voltage spike. Gain past eleven, something in the chain gives, and the result is a pitch the equipment was not designed to make. This is the one we are here for.
Feedback is rebel expression because it is unrepeatable, and everything the industry sells is a promise of repetition. The howl says: this room, this night, this body. Then it is gone.