Suppose you record a song on magnetic tape and duplicate your recording. You then simultaneously play back both tapes. To the rim of one of the tape reels, also known as the reel's flange, you keep applying gentle pressure and then releasing that pressure so that your reel alternates between slightly lagging the other and then catching up with it. The resulting small pitch differences between the two tapes give rise to an intriguing and pleasant sound often described as swirling or jet-like. A Wikipedia article1 lists dozens of popular songs that incorporate this “flanging” effect. Well represented are songs by the Beatles and Jimi Hendrix as well as by artists from recent decades. But perhaps the most important is an obscure 1945 recording by guitarist and musical inventor Les Paul, who is recognized as the discoverer of flanging.

Topics
Magnetic devices, Human voice, Pitch, Tuning forks, Acoustic waves, Wave forms, Mechanical instruments, Fourier analysis, Educational aids, Education
6.
Supplementary QuickTime movie of beating sawtooth waves can be seen at http://dx.doi.org/10.1119/1.4914569_1.
7.
Supplementary QuickTime movie of beating square waves can be seen at http://dx.doi.org/10.1119/1.4914569_2.
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2015
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