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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 electronic mixer 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 , an approach developed in the 1940s and 1950s and used by artists including Elvis Presley and Buddy Holly.
Analog effects units were introduced in the 1970s; digital effects pedals in 1984; and audio plug-in software in the 2000s.
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.
With the Roland RE-201, introduced in 1973, Japanese engineer Ikutaro Kakehashi refined the tape delay to make it more reliable and robust, with reduced tape wear and noise, wow, and flutter, additional controls, and additional tape heads. Different effects could be created by enabling different combinations of playback heads. By adjusting the controls and tape speed, musicians could create pitch-shifting and oscillated effects. The RE-201 was used by acts including Brian Setzer, Bob Marley, Portishead, and Radiohead.
In the 1970s, Jamaican dub reggae producers used delay effects extensively; Lee "Scratch" Perry created "lo-fi sci-fi" effects by using delay and reverb effect on a mixing console test tone and dub techno producers such as Basic Channel introduced delay to electronic music. Digital delay effects were developed with the arrival of digital recording.
Delay processors based on analog tape recording use magnetic tape as their recording and playback medium. Electric motors guide a tape loop through a device with a variety of mechanisms allowing modification of the effect's parameters. Popular models include Ray Butts' EchoSonic (1952), the Watkins Copicat (1958), the Echoplex (1959) and the Roland Space Echo (1974).
In the Echoplex EP-2, the play head position was fixed, while a combination record and erase head was mounted on a slide, thus the delay time of the echo was adjusted by changing the distance between the record and play heads.
The Space Echo uses a free-running tape transport system to reduce tape wear, noise, and wow and flutter, and made the units more reliable and easy to transport. It was more reliable and sturdy than previous tape echo devices, making it easy to travel and perform with. It has been used by musicians in genres such as reggae, Dub music, trip hop, post-punk and experimental rock.
Thin magnetic tape was not entirely suited for continuous operation, however, so the tape loop has to be replaced from time to time to maintain the High fidelity of the processed sounds. The Binson Echorec used a rotating magnetic drum or disc (not entirely unlike those used in modern hard disk) as its storage medium. This provided an advantage over tape, as the durable drums were able to last for many years with little deterioration in the audio quality. In later years, tape delay effects remained popular for the way the tape compresses and distorts, "creating the impression that the echoes are receding rather than just getting quieter".
Invented by Ray Lubow, the oil-can method uses a rotating disc of anodized aluminium coated with a suspension of carbon particles. An AC signal to a conductive neoprene wiper transfers the charge to the high impedance disc. As the particles pass by the wiper, they act as thousands of tiny capacitors, holding a small part of the charge. A second wiper reads this representation of the signal, and sends it to a voltage amplifier that mixes it with the original source. To protect the charge held by the particles and to lubricate the entire assembly, the disc runs inside a sealed can with enough of a special insulating oil to assure that an even coating is applied as it spins.
The effect resembles an echo, but the whimsical nature of the storage medium causes variations in the sound that can be heard as a vibrato effect. Some early models featured control circuitry designed to feed the output of the read wiper to the write wiper, causing a reverberant effect as well.
Many different companies marketed these devices under various names. Fender sold the Dimension IV, the Variable Delay, the Echo-Reverb I, II, and III, and included an oil can in their Special Effects box. Gibson sold the GA-4RE from 1965–67. Ray Lubow himself sold many different versions under the Tel-Ray/Morley brand, starting out in the early sixties with the Ad-n-echo, and eventually producing the Echo-ver-brato, the Electrostatic Delay Line, and many others into the eighties.
Digital delay effects were initially available as expensive rack-mounted units intended for use in television and audio production studios. One of the first was the Eventide DDL 1745 from 1971. Another popular rack-mount digital delay was the AMS DMX 15-80 of 1978. As digital memory became cheaper in the 1980s, units like Lexicon PCM42, Roland SDE-3000, TC Electronic 2290 offered more than three seconds of delay time, enough to create background loops, rhythms, and phrases. The 2290 was upgradeable to 32 seconds and Electro-Harmonix offered a 16-second delay and looping machine. Eventually, as costs came down further and the electronics grew smaller, they became available in the form of foot pedals. The first digital delay offered in a pedal was the Boss Corporation DD-2 in 1984. Rack-mounted delay units evolved into digital reverb units and on to digital multi-effects units capable of more sophisticated effects than pure delay, such as reverb and audio time stretching and pitch scaling effects.
Digital delays present an extensive array of options, including control over the time before playback of the delayed signal. Most also allow the user to select the overall level of the processed signal in relation to the unmodified one, or the level at which the delayed signal is fed back into the memory, to be repeated again. Some systems allow more exotic controls, such as the ability to add an audio filter and modulate the playback rate.
John Martyn was a pioneer of the Echoplex. Perhaps the earliest indication of his use can be heard on the songs "Would You Believe Me" and "The Ocean" on the album Stormbringer! released in February 1970.
Most delay effects allow users to set the delay time, or the amount of time between each audio playback. The may be synchronized to a BPM, allowing users to set time values as . Delay is used to create other effects, including reverb, chorus effect, and flanging.
Delay effects typically allow users to add and adjust feedback. By feeding some of the delayed audio back into the delay mechanism, multiple repeats of the audio are heard. At low feedback settings, each repeat fades in volume. High levels of feedback can cause the level of the output to rapidly increase, becoming louder and louder; this may be managed using a limiter.
Straight delay is also used in audio to video synchronization to align sound with visual media (e.g., on TV or web broadcasting), if the visual source is delayed. Visual media can become delayed by a number of mechanisms or reasons such as time base correction, video scaling and , in which case the associated audio may be delayed to match the visual content.
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