Sound
Transient response
Also called attack, speed, transients
Transient response is how quickly and cleanly a product reproduces the start of a sound: a drum stick on a rim, a plucked string, a consonant. Fast transients sound crisp; slow ones sound soft or smeared.
A transient is a brief burst of energy with a sharp leading edge. Planar and Electrostatic designs are often described as fast, which owners put down to their light diaphragms. Many engineers counter that for most drivers the transient behavior follows from the frequency response, so "speed" is largely treble extension and low ringing.
The flip side is Decay, how a sound fades. Together they decide whether a product sounds lively or sluggish, and both are part of what listeners call Dynamics.
Treble emphasis can imitate speed, so a sharp-sounding product is not always a fast one.