Flanging /ˈflændʒɪŋ/ is an audio effect produced by mixing two identical signals together, one signal delayed by a small and (usually) gradually changing period, usually smaller than 20 milliseconds. This produces a swept comb filter effect: peaks and notches are produced in the resulting frequency spectrum, related to each other in a linear harmonic series. Varying the time delay causes these to sweep up and down the frequency spectrum. A flanger is an effects unit that creates this effect.
Part of the output signal is usually fed back to the input (a re-circulating delay line), producing a resonance effect that further enhances the intensity of the peaks and troughs. The phase of the fed-back signal is sometimes inverted, producing another variation on the flanger sound.
As an audio effect, a listener hears a drainpipe or swoosh or jet plane sweeping effect as shifting sum-and-difference harmonics are created analogous to use of a variable notch filter. The term "flanging" comes from one of the early methods of producing the effect. The finished music track is recorded simultaneously to two matching tape machines, then replayed with both decks in sync. The output from the two recorders is mixed to a third recorder. The engineer slows down one playback recorder by lightly pressing a finger on the flange (rim) of the supply reel. The drainpipe or subtle swoosh effect sweeps in one direction, and the playback of that recorder remains slightly behind the other when the finger is removed. By pressing a finger on the flange of the other deck, the effect sweeps back in the other direction as the decks progress towards being in sync. The Beatles' producer George Martin disputed this reel flange source, attributing the term to himself and John Lennon instead.[1][2]
Despite claims over who originated flanging, Les Paul discovered the effect in the late 1940s and 1950s; however, he did most of his early phasing experiments with acetate disks on variable-speed record players. On "Mammy's Boogie" (1952) he used two disk recorders, one with a variable speed control.[3][4] The first hit song with a very discernible flanging effect was "The Big Hurt" (1959) by Toni Fisher.[5]
Further development of the classic effect is attributed to Ken Townsend, an engineer at EMI's Abbey Road Studio, who devised a process in the spring of 1966. Tired of laboriously re-recording dual vocal tracks, John Lennon asked Townsend if there was some way for the Beatles to get the sound of double-tracked vocals without doing the work. Townsend devised artificial double tracking (ADT). According to historian Mark Lewisohn, it was Lennon who first called the technique "flanging". Lennon asked George Martin to explain how ADT worked, and Martin answered with the nonsense explanation "Now listen, it's very simple. We take the original image and we split it through a double vibrocated sploshing flange with double negative feedback".[1] Lennon thought Martin was joking. Martin replied, "Well, let's flange it again and see". From that point, when Lennon wanted ADT he would ask for his voice to be flanged, or call out for "Ken's flanger". According to Lewisohn, the Beatles' influence meant the term "flanging" is still in use today, more than 50 years later. The first Beatles track to feature flanging was "Tomorrow Never Knows" from Revolver, recorded on 6 April 1966. When Revolver was released on 5 August 1966, almost every song had been subjected to flanging.[6]
Others have attributed it to George Chkiantz, an engineer at Olympic Studios in Barnes, London. Another flanging instance on a rock-era pop recording occurs in the Small Faces' 1967 single "Itchycoo Park",[7] recorded at Olympic and engineered by Chkiantz's colleague Glyn Johns.