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Flanging // is an audio effect produced by mixing two identical signals together, one signal delayed by a small and 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 which 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 playback-head output from the two recorders is mixed to a third recorder. The engineer slows down one recorder by lightly pressing a finger on the flange (rim) of one of the playout reels. The "drainpipe" or subtle "swoosh" 'flange flango' 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 has disputed this "reel flange" source, instead attributing the term to John Lennon (see Martin's account below.)
Older recording hardware could suffer flanging as a side effect when recording long tracks. As the weight of the tape built on one reel, the pressure on the capstans caused flanging in mixdown or dubbing. This was a problem faced by studio engineers in the 1960s and 1970s when recording large concept pieces, as explained by Ian Anderson of Jethro Tull when recounting the studio challenges of recording Thick as a Brick.
Despite subsequent 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. His 1955 single "Nuevo Laredo" features phase shifting, as does the 1953 single "Mammy's Boogie." 
American music industry veterans David S. Gold and Stan Ross, founders of Gold Star Studios in Hollywood, claim they made the first commercial recording—the single "The Big Hurt" by Toni Fisher—at Gold Star in late 1959 and a hit in the United States in early 1960, rising to #3 on Billboard magazine's singles chart. Flanging is also heard in the opening of The Ventures' 1962 cover of The Tornados' "Telstar", in a rocket launch sound effect.
Further development of the classic effect is attributed to Ken Townsend, an engineer at EMI's Abbey Road Studio, who devised the 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 or 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". 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 40 years later. The first Beatles track to feature flanging was "Tomorrow Never Knows" from Revolver, which was recorded on April 6, 1966. When Revolver was released on August 5, 1966, almost every song had been subjected to flanging.
Others have attributed it to George Chkiantz, an engineer at Olympic Studios in Barnes, London. One of the first instances on a pop recording was The Small Faces' 1967 single "Itchycoo Park", recorded at Olympic and engineered by Chkiantz's colleague Glyn Johns.
The first stereo flanging is credited to producer Eddie Kramer, in the coda of Jimi Hendrix's "Bold as Love" (1967). Kramer said in the 1990s that he read BBC Radiophonic Workshop journals for ideas and circuit diagrams.
In 1968, the record producer for The Litter, Warren Kendrick, devised a method to precisely control flanging by placing two 15 IPS (inches per second) stereo Ampex tape recorders side by side. The take-up reel of recorder A and supply reel of B were disabled, as were channel 2 of recorder A, channel 1 of recorder B and the erase head of recorder B. The tape was fed left-to-right across both recorders and an identical signal was recorded on each channel of the tape, but displaced by approximately 18 inches along the length of the tape. During recording, an ordinary screwdriver was wedged between the recorders to make the tape run "uphill" and "downhill." The same configuration was employed during the playback/mixdown to a third recorder. The screwdriver was moved back and forth to cause the two signals to diverge, then converge. The latter technique permits zero point flanging; i.e., the lagging signal crosses over the leading signal and the signals change places.
A similar "jet plane-like" effect occurs naturally in long distance shortwave radio music broadcasts. In this case the varying delays are caused by varying radio wave propagation times and multipath radio interference.
In the 1970s, advances in solid-state electronics made flanging possible using integrated circuit technology. Solid-state flanging devices fall into two categories: analog and digital. The flanging effect in most newer digital flangers relies on DSP technology. Flanging can also be accomplished using computer software.
The original tape-flanging effect sounds a little different from electronic and software recreations. Not only is the tape-flanging signal time-delayed, but response characteristics at different frequencies of the tape and tape heads introduced phase shifts into the signals as well. Thus, while the peaks and troughs of the comb filter are more or less in a linear harmonic series, there is a significant non-linear behaviour too, causing the timbre of tape-flanging to sound more like a combination of what came to be known as flanging and phasing.
"Barber pole" flanging
Also known as "infinite flanging", this sonic illusion is similar to the Shepard tone effect, and is equivalent to an auditory "barber pole". The sweep of the flanged sound seems to move in only one direction ("up" or "down") infinitely, instead of sweeping back-and-forth. While Shepard tones are created by generating a cascade of tones, fading in and out while sweeping the pitch either up or down, barber pole flanging uses a cascade of multiple delay lines, fading each one into the mix and fading it out as it sweeps to the delay time limit. The effect is available on various hardware and software effect systems.
Comparison with phase shifting
Flanging is one specific type of phase-shifting, or "phasing". In phasing, the signal is passed through one or more all-pass filters with non-linear phase response and then added back to the original signal. This results in constructive and destructive interference that varies with frequency, giving a series of peaks and troughs in the frequency response of the system. In general, the position of these peaks and troughs do not occur in a harmonic series.
In contrast, flanging relies on adding the signal to a uniform time-delayed copy of itself, which results in an output signal with peaks and troughs which are in a harmonic series. Extending the comb analogy, flanging yields a comb filter with regularly spaced teeth, whereas phasing results in a comb filter with irregularly spaced teeth.
In both phasing and flanging, the characteristics (phase response and time delay respectively) are generally varied in time, leading to an audible sweeping effect. To the ear, flanging and phasing sound similar, yet they are recognizable as distinct colorations. Commonly, flanging is referred to as having a "jet-plane-like" characteristic. In order for the comb filter effect to be audible, the spectral content of the program material must be full enough within the frequency range of this moving comb filter to reveal the filter’s effect. It is more apparent when it is applied to material with a rich harmonic content, and is most obvious when applied to a white noise or similar noise signal. If the frequency response of this effect is plotted on a graph, the trace resembles a comb, and so is called a comb filter.
Flanging is a time-based effects unit that occurs when two identical signals are mixed together, but with one signal time-delayed by a small and gradually changing amount, usually smaller than 20 milliseconds. This produces a swept comb filter effect: peaks and notches are produced in the resultant 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.
Part of the output signal is usually fed back to the input (a re-circulating delay line), producing a resonance effect which further enhances the intensity of the peaks and troughs. The phase of the fed-back signal is sometimes inverted, producing another variation on the flanging sound.
A flanger is a device dedicated to creating this sound effect. Examples of music recordings with a flanging effect include:
- "Mammy's Boogie" (1952) by Les Paul. Paul invents the technique in his garage studio using two disk recorders, one with a variable speed control.
- "The Big Hurt" (1959) by Toni Fisher – first hit song with a very discernible flanging effect.
- "From Me to You" (1963) by The Beatles – flanging can be heard during a drum fill immediately before the first verse; this came unintentionally during the process of overdubbing harmonica onto the track.
- "It's Gonna Rain" (1965) by Steve Reich – a flanging effect is among those used on this experimental loop-based tape piece.
- "The Big Hurt" (1966) by Del Shannon – a flanging effect was also heard on this cover version.
- "Lucy in the Sky with Diamonds" (1967) by The Beatles from the album Sgt. Pepper's Lonely Hearts Club Band.
- "Itchycoo Park" (1967) by the Small Faces, psychedelic interludes between chorus and verse (0:50–1:07, 1:40–2:05, 2:20–2:46). The 1st British single to feature tape flanging (phasing) to accentuate its overt drug references.
- "Bold as Love" (1967) from the album Axis: Bold as Love by The Jimi Hendrix Experience – the first use of stereo phasing, done by engineer George Chkiantz, is heard during the coda of the song (2:47)
- "Blue Jay Way" from the album Magical Mystery Tour (1967) by The Beatles
- "Green Tambourine" (1967) by The Lemon Pipers
- "Pictures of Matchstick Men" (1968) by Status Quo
- "Rainbow Chaser" (1968) by Nirvana (UK band), phasing throughout the song.
- "Open My Eyes" by The Nazz from the album The Nazz (1968), featuring Todd Rundgren.
- "Sky Pilot" (1968) by The Animals
- "This Wheel's on Fire" (1968) by Julie Driscoll with Brian Auger and the Trinity
- Strictly Personal (1968) by Captain Beefheart, significant flanging effects on drums, vocals, etc. on the album.
- "Old John Robertson", and "Wasn't Born to Follow", by The Byrds, on the album The Notorious Byrd Brothers (1968).
- Electric Ladyland (1968) by Jimi Hendrix
- Uncle Charlie & His Dog Teddy (1970) by the Nitty Gritty Dirt Band
- The Man Who Sold the World (1970) by David Bowie
- DJ Walter Gibbons, at the Galaxy 21 night club on 23rd Street near the Hotel Chelsea in Manhattan (open from 1972–1976), was phasing records-playing two records at the same time to create a flange effect. The technique was picked up by future skilled DJs.
- "Listen to the Music", from the album Toulouse Street (1972) by The Doobie Brothers
- "This Flight Tonight", from the album Loud 'n' Proud (1973) by Nazareth (covering song by Joni Mitchell) produced by Roger Glover, song features extensive use of an E-Bow on the lead guitar track with tape-flanging applied.
- "Bridge of Sighs" (1974) by Robin Trower – using a Univox Univibe.
- "Killer Queen" from the album Sheer Heart Attack (1974) by Queen, reel tape phasing on the vocal line "a laser beam". Also, the second "wanna try", and the fade-out at the end of the song.
- "Daddy Don't Live In That New York City No More" from the album Katy Lied (1975) by Steely Dan, on Donald Fagen's lead vocal.
- "Evil Woman" from the album Face the Music (1975) by Electric Light Orchestra, on the string interlude before the third chorus (a reversed string section from "Nightrider").
- "Station to Station" (1976) by David Bowie, flanging on the minute-long opening train sound effect.
- "I Feel Love" (1977) by Donna Summer. Producers Giorgio Moroder and Pete Bellotte use a flange effect on the Top 10 disco hit.
- Low (1977) and "Heroes" (1977), including the track "V-2 Schneider" by David Bowie
- "Life in the Fast Lane" (1977) by The Eagles, on the bridge (3:38) of the song.
- Trans-Europe Express (1977) by Kraftwerk, using an Eventide FL-201 Instant Flanger
- "Hong Kong Garden" (1978) by Siouxsie and the Banshees. Guitarist John McKay uses an MXR flanger.
- Reggatta de Blanc (1979) by The Police. Guitarist Andy Summers sets a light flange on his guitar using an Electro-Harmonix Electric Mistress pedal.
- "Memories of Green" from the album See You Later (1980) by Vangelis. A Steinway grand piano was put through an Electro-Harmonix Electric Mistress flanger pedal. The effect is used throughout the piece.
- "And the Cradle Will Rock..." (1980) on guitar and electric piano, and "Unchained" (1981) on guitar by Van Halen, using an MXR Flanger
- "Drowning Witch" (1982) from the album Ship Arriving Too Late to Save a Drowning Witch by Frank Zappa, using a MicMix Dynaflanger on the guitar.
- "Made of Stone" (1989) by The Stone Roses, on the bridge riff (3:30).
- "Money Can't Buy It" from the album Diva (1992) by Annie Lennox, on the lead vocal on the bridge.
- "Popscene" (1992) by Blur, on the opening/main guitar riff.
- "Curmudgeon", "Scentless Apprentice", "Radio-Friendly Unit Shifter" (1993) by Nirvana, using an Electro-Harmonix poly chorus on the guitar.
- "Bring It On" from the album Seal (1994) by Seal, on the lead vocal during the bridge.
- "Bad Horsie" from the EP Alien Love Secrets (1995) by Steve Vai, the end of the song uses a real tape flange.
- Feeling This (2003) by Blink-182, Although computer technology offered it during the album’s production, according to Hoppus, the band opted to produce the effect "the old school way", opting for two tape machines
- Morningwood (2006) by Morningwood, on many of the guitar parts.
- "Dani California" (2006) by the Red Hot Chili Peppers, tape phasing on the drum fill that segues into the guitar solo (3:47).
- "Crazy Horse" (2010) by Black Label Society; guitarist Zakk Wylde used an Eddie Van Halen flanger on the main guitar riff
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