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The name originates from the original method of creation which involved playing the same recording on two synchronized tape recorders with the output of one machine out of phase as above, and then mixing the two output signals together. As long as the machines are perfectly synchronized, the result will be silence, as the signals will be cancelling each other out. Given the near-impossibility of keeping two analog tape decks perfectly in sync, however, this silence is only be achieveable for a split second before the signals slip slowly out of sync again. If the operator places his/her finger on the flange (that is to say, the rim) of one of the tape reels, that machine can be made to slow down, slipping out of sync by tiny degrees. A listener will hear the familiar "drainpipe" swooping effect as shifting sum-and-difference harmonics are created.
If the frequency response of this effect is plotted on a graph, the trace resembles a comb, and so is called a comb filter. Once the operator takes his/her finger off, that player will speed up until its tachometer is back in phase with the master, and as this happens, the flanging effect will be repeated, with the harmonics swooping gradually higher until both signals pass momentarily through the silent perfect sync point again. It is often aesthetically better not to let the two tapes reach this point, but to start the reel-slowing again just before they get back into sync.
In the 1970s, advances in solid state electronics made the flanging effect 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. Even today, though, many studio practitioners prefer the sound of analog tape flanging, finding the serendipitous nature of human intervention more interesting than the clinical perfection created by purely electronic means. Tape flanging requires bulky hardware and takes quite a knack to get right, but the results are well worth the time and effort.
This entry has been amended by Ken Cumberlidge