An electronic circuit which delays the passage of a signal through it, such that any given signal that is applied to the input will appear at the output after a precise amount of time has elapsed. Delay lines may be digital or analog in nature. Contemporary analog delays are solid-state and are based on bucket brigade devices. Prior to about 1990, tape echo units were commonly used for this purpose.
When the output of a delay line is mixed with the original signal, a variety of audio effects are produced, depending to a considerable extent on the delay time. These can be divided into five broad categories:
- 0-10 milliseconds: Flanging
- 10-25 milliseconds: Chorusing
- 25-80 milliseconds: Doubling or ensemble effect
- 80 mililliseconds-2 seconds: Echo
- > 2 seconds: Sound-on-sound; the delayed sound is no longer perceived as an echo (see Soundscapes)