An effect used mostly in the 1950s and 60s to produce a form of pitch shifting and time compression. Many professional tape machines of the era offered two or three choices of recording and playback speed, which for mechanical reasons typically would be multiples, e.g., 3-3/4, 7-1/2, and 15 inches per second (ips). Since they were multiples, recording at one speed and selecting a different speed for playback would raise or lower the playback by an octave.
In the double-speed recording technique, the performer recorded the part at a slow speed, and then played back at the next faster speed, which had the effect of raising the pitch by an octave, and doubling the tempo. It was necessary for the performer to perform an octave lower than the intended playback pitch, and matching the tempo at slow speed could be tricky. Nonetheless, the technique could produce effects very much like a pitch shifter. David Seville used the technique extensively to record his own singing for his series of "Alvin and the Chipmumks" novelty songs in the 1960s, to produce munchkinized vocals. In the 1970s, some bands used it to record "impossible" guitar solos; the guitarist would play at normal tempo but an octave lower and for twice the number of measures intended, and the resulting playback doubled the tempo while producing a normal-length solo.