Time varying delay – Frippertronics and crafty guitarists


Robert Fripp (King Crimson, The League of Crafty Guitarists, League of Gentlemen, solo artist…) is known as one of the greatest and most influential guitarists of all time.  Evolving out of his work with Brian Eno in 1973, he devised a tape looping technique to layer his guitar sounds in real-time. It used two reel-to-reel tape recorders. The tape traveled from the supply reel of one recorder to the take-up reel of the second one. Then the tape from the second machine is fed back to the first one, and the delay can be changed by adjusting the distance between the two machines. Furthermore, it also provided a recording of the complete overlayed recording, and could be used in live performance. Fripp’s girlfriend later named this technique ‘Frippertronics,’ though we would describe it as a time varying delay with feedback. Also among Robert Fripp’s more unusual contributions, are many of the sounds for the Windows Vista operating system.

Many other famous guitarists are also known for music technology innovations. For instance, Tom Scholz of the band Boston designed a wide range of novel guitar effects devices, including the Rockman amplifier. But one of the most famous guitarists is also one of the people who most influenced music technology, Les Paul. His solid body electric guitar designs were some of the first and most popular, and he is credited with many innovations in multrack recording.

Double vibrocated sploshing flange

Ken’s Flanger

Flanging is an unusual name for an audio effect, and its certainly not a common word in music or signal processing. The flange refers to a rim or edge, especially on a tape reel. Producers were known to manipulate the flange of a tape reel to achieve nice effects on many early tape recordings. One of the earliest known examples of producing a sound similar to the modern flanger is ‘The Big Hurt’ by Tony Fisher, recorded in 1959.

But the origin of the name of the audio effect is an unusual one, and has been well documented by Beatles historians Bill Biersach and Mark Lewisohn.

In 1966, the Beatles recorded Revolver at Abbey Road. The studio technician Ken Townsend later said that “they would relate what sounds they wanted and we then had to go away and come back with a solution… they often liked to double-track their vocals, but it’s quite a laborious process and they soon got fed up with it. So, after one particularly trying night-time session doing just that, I was driving home and suddenly had an idea.”

What Townsend devised was not the modern flanging, but the closely related chorus effect, or artificial double tracking (ADT). But its implemented using the same approach, slowing down and speeding up a tape machine. The seemingly random variations in speed (and hence also pitch) mimic the effect of a singer trying to harmonise with the original.

John Lennon loved the effect, and asked George Martin, the Beatles producer, to explain it. As Martin recalled, “I knew he’d never understand it, so I said, ‘Now listen, it’s very simple. We take the original image and split it through a with double negative feedback …’ He said, ‘You’re pulling my leg, aren’t you?’ I replied, ‘Well, let’s flange it again and see.’ From that moment on, whenever he wanted it he’d ask for his voice to be ‘flanged,’ or call out for ‘Ken’s flanger.’ ”


  • M. Lewisohn, The Beatles Recording Sessions. New York: Harmony Books (Crown Publishers), 1989.
  • G. Martin and W. Pearson, Summer of Love: The Making of Sgt Pepper. London: Pan Books, 1994.

Why 44.1 kHz?

Why is  44.1 kHz the standard sample rate in consumer audio?
44.1 kHz, or 44,100 samples persecond, is perhaps the most popular sample rate used in digital audio, especially for music content. The short answer as to why it is so popular is simple; it was the sample rate chosen for the Compact Disc, and thus is the sample rate of much audio taken from CDs, and the default sample rate of much audio workstation software.
As to why it was chosen as the sample rate for the Compact Disc, the answer is a bit more interesting. In the 1970s, when digital recording was still in its infancy, many different sample rates were used, including 37kHz and 50 kHz in Soundstream’s recordings. In the late 70s, Philips and Sony collaborated on the Compact Disc, and there was much debate between the two companies regarding sample rate. In the end, 44.1 kHz was chosen for a number of reasons.
According to the Nyquist theorem, 44.1 kHz allows reproduction of all frequency content below 22.05 kHz. This covers all frequencies heard by a normal person. Though there is still debate about perception of high frequency content, it is generally agreed that few people can hear tones above 20 kHz.
44.1 kHz also allowed the creators of the CD format to fit at least 80 minutes of music (more than on a vinyl LP record) on a 120 millimeter disc, which was considered a strong selling point.
But 44,100 is a rather special number. 44,100 = 2x2x3x3x5x5x7x7, and hence 44.1kHz is actually an easy number to work with for many calculations.

Welcome to our blog

Hi everyone, and welcome to our new blog, provisionally titled ‘Intelligent Sound Engineering.’ We are the Audio Engineering research team within the Centre for Digital Music at Queen Mary University of London.

This blog is for us to discuss anything of interest to us. It will touch on research subjects like audio effects, sound synthesis, music production, acoustics, psychoacoustics, intelligent systems design and more. But we’ll also chat about any interesting news items, what we (or our colleagues) have been doing, and what it is like to be engaged in academic research.

Don’t forget to check out our youtube channel, IntelligentSoundEng, with around 50 videos.

Please get in touch.