Delay Handout

A delay takes a signal and plays it back after a certain amount of time. Although delay is very simple, it is a great way to animate sounds that might be dull or uninteresting. Delay is the basic ingredient to a vast array of audio processing techniques, from the very simple (echo, reverberation), to the very complex (comb filtering, flange, and chorus).

There are two ways to set up a delay:

Feed-forward – the direct signal goes forward around the delayed signal and combines with the delayed output (FIR)

feed_forward

(Wikipedia)
Feedback – brings the signal back to the input (IIR)

feed_back

(Wikipedia)

Here is a chart to give an idea of the delay times with each effect:

table

Chorus – the same basic principle as a chorus of singers. This effect causes the instrument’s sound to become more full as if there is more than one instrument being played. A chorus of singers will not always be on the exact same pitch at the same time. In the same way, the chorus effect causes the pitch to slightly fluctuate giving the instrument a fuller sound.

Flanging – gives off a swooshing sound, similar to the sound of a jet plane is passing by. Flanging is created by mixing a dry signal with a slightly delayed version of the same signal. Although there is a delayed signal, it cannot be perceived because the signal is only delayed by around 10 milliseconds.

Comb Filter – basic building block for building audio effects. A comb filter adds a delayed signal to the original signal.

Innovators:

Multi Track Tape Recorder – developed by Les Paul in the early 40’s and improved by Raymond Scott, the multi-track tape recorder was used to develop the techniques such as tape delay and flange. It allows for numerous audio signals to be recorded onto one reel of tape.

Tape Delay – Created by recording a signal onto an analogue tape and then playing it back through the input. This would cause the tape recorder to record and play back the sound at the same time. The speed and distance between the tape head and record head would determine the delay. Pauline Oliveros was an influential innovator in tape delay in the early 60’s. She mainly used tape delay to mix sounds together as a means of making a rhythmic background for her music. Oliveros used numerous tape recorders to create multiple echoes at the same time using the same input. Because of the different tape recorders, different timbres and delay times would result.

Here are sound bits of tape delay being heard in Oliveros' piece, "Bye Bye Butterfly"
Sample 1
Sample 2

Flange – the development of flange can be credited to Ken Townshend in 1966. At EMI’s Abbey Road studio, he was asked by John Lennon to find a way to get the sound of double tracked vocals without actually tracking the vocals twice. Townshend developed the Artificial Double Tracking and Lennon dubbed it as the “Flanger”. It worked by recording a signal to two different tape machines at the same time. By combining these recordings onto one tape, there would be very small differences between each other created a phasing effect. The engineer would then press his finger on the rim of the tape reel so the tape would slow down out of sync with the other tape. This would cause the swooshing flange effect. The engineer would then take his finger off the tape and the swooshing flange effect would move back the other direction back into sync with the other tape.

The first song that the Beatles incorporated flange into is "Tomorrow Never Knows" from their album Revolver. You can listen to this song and hear the flange effect here.

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