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What is Delay?

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 processed audio is blended with the unprocessed 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. Analog effects units were introduced in the 1970s; digital effects pedals in 1984; and audio plug-in software in the 2000s. Delay effects add a time delay to an audio signal. When the wet (processed) audio is blended with the dry (unprocessed) audio, it creates an echo-like effect, whereby the original audio is heard followed by the delayed audio. Delay effects typically allow users to adjust the amount of feedback. By feeding some of the delayed audio back into the buffer, multiple repeats of the audio play back (feedback). At low feedback settings, each repeat fades in volume. High levels of feedback can cause the level of the output to rapidly increase (self-oscillation), becoming louder and louder; this may be managed with limiters. The delayed signal may be treated separately from the input audio - for example, with an equalizer. Most delay effects also 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 beat divisions.[5] Delay is used to create other effects, including reverb, chorus and flanging. Digital delay effects record a sample of audio and play it back. Software versions record the audio to a buffer. Digital delay may also modify the recorded sound, by reversing it, altering its pitch, or other manipulations. Some digital delays emulate the "gritty, grainy" sound of earlier delay effects. Haas effect Edit Short delays (50ms or less) create a sense of "broadening" the sound without creating a perceptible echo, and can be used to add stereo width or simulate double-tracking (layering two performances).The effect is known as the Haas effect after the German mathematician Helmut Haas. Ping-pong delay Edit In a ping-pong delay, the delayed signal alternates between two stereo channels. Multi-tap Edit In a multi-tap delay, multiple "taps" (outputs) are taken from a delay buffer, each with independent times and levels, and summed with the original signal Multi-tap delays be used to create rhythmic patterns or dense, reverb-like effects. Doubling echo Edit Doubling echo is produced by adding short delay to a recorded sound. Delays of thirty to fifty milliseconds are the most common; longer delay times become slapback echo. Mixing the original and delayed sounds creates an effect similar to doubletracking, or unison performance. Slapback echo Edit Slapback echo uses a longer delay time (60 to 250 milliseconds), with little or no feedbackA slapback delay creates a thickening effect. The effect is characteristic of vocals on 1950s rock-n-roll records. l The effect was produced by re-feeding the output signal from the playback head tape recorder to its record head. The physical space between heads, the speed of the tape, and the chosen volume being the main controlling factors. Analog and later digital delay machines also easily produced the effect. It is also sometimes used on instruments, particularly drums and percussion. Straight delay Straight delay is used in sound reinforcement systems; a straight delay is used to compensate for the propagation of sound through the air. Unlike audio delay effects devices, straight delay is not mixed back in with the original signal. The delayed signal alone is sent to loudspeakers so that the speakers distant from the stage, as in a large outdoor rock festival, will reinforce the stage sound at the same time or slightly later than the acoustic sound from the stage. The delayed signal uses approximately 1 millisecond of straight delay per foot of air or 3 milliseconds per meter, depending on the air temperature's effect on the speed of sound.[c] Because of the Haas effect, this technique allows audio engineers to use additional speaker systems placed away from the stage and still give the illusion that all sound originates from the stage. The purpose is to deliver sufficient sound volume to the back of the venue without resorting to excessive sound. 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, in which case the associated audio must be delayed to match the visual content.