Delay (audio effect)

Delay is an audio signal processing technique that records an input signal to a storage medium and then plays it back after a period of time. When the delayed playback is mixed with the live audio, it creates an echo-like effect, whereby the original audio is heard followed by the delayed audio. The delayed signal may be played back multiple times, or fed back into the recording, to create the sound of a repeating, decaying echo.

Delay effects range from a subtle echo effect to a pronounced blending of previous sounds with new sounds. Delay effects can be created using tape loops, an approach developed in the 1940s and 1950s and used by artists including Elvis Presley and Buddy Holly.^{[citation needed]}

Analog effects units were introduced in the 1970s; digital effects pedals in 1984; and audio plug-in software in the 2000s.^{[citation needed]}

The first delay effects were achieved using tape loops improvised on reel-to-reel audio tape recording systems. By shortening or lengthening the loop of tape and adjusting the read-and-write heads, the nature of the delayed echo could be controlled. This technique was most common among early composers of musique concrète such as Pierre Schaeffer, and composers such as Karlheinz Stockhausen, who had sometimes devised elaborate systems involving long tapes and multiple recorders and playback systems, collectively processing the input of a live performer or ensemble.

American producer Sam Phillips created a slapback echo effect with two Ampex 350 tape recorders in 1954. The effect was used by artists including Elvis Presley (such as on his track "Blue Moon of Kentucky") and Buddy Holly, and became one of Phillips' signatures. Guitarist and instrument designer Les Paul was an early pioneer in delay devices. According to Sound on Sound, "The character and depth of sound that was produced from tape echo on these old records is extremely lush, warm and wide."

Tape echoes became commercially available in the 1950s. Tape echo machines contain loops of tape that pass over a record head and then a playback head. An echo machine is the early name for a sound processing device used with electronic instruments to repeat the sound and produce a simulated echo. The time between echo repeats was adjusted by varying head position or tape speed. The length or intensity of the echo effect was adjusted by changing the amount of echo signal was fed back into the signal recorded to tape.

A landmark device was the EchoSonic made by American Ray Butts. It is a portable guitar amplifier with a built-in tape echo, which became used widely in country music (Chet Atkins) and especially in rock and roll (Scotty Moore).

Dedicated machines for creating tape loops were introduced One example is the Echoplex which uses a tape loop. The length of delay is adjusted by changing the distance between the tape record and playback heads. Another is the Ace Tone EC-1 Echo Chamber.