Reamping

The guitar is tracked through a DI box, often alongside a miked amp as a reference. Later the dry track is sent out of the audio interface and back into an amp, which is miked up and recorded again. The tone can be changed after the fact without the guitarist replaying a note — only the amp, the mic position and the room change.

The catch is that a line output has low impedance and a hot level, while a guitar amp expects the opposite. A reamp box — a term engineer John Cuniberti turned into a product name in the nineties — drops the level, raises the impedance and breaks the ground loop with a transformer. These days the same job is often done entirely in the computer with amp simulation and speaker-cabinet impulse responses.