Pitch shifting is a sound recording technique in which the original pitch of a sound is raised or lowered. Effects units that raise or lower pitch by a pre-designated musical interval (transposition) are called pitch shifters.
The simplest methods are used to increase pitch and reduce durations or, conversely, reduce pitch and increase duration. This can be done by replaying a sound waveform at a different speed than it was recorded. It could be accomplished on an early reel-to-reel tape recorder by changing the diameter of the capstan or using a different motor. As technologies improved, motor speeds could be controlled by electronic servo system circuits. This arrangement using “vari-speed” capstan motors allowed the speed change to be achieved more simply. As for vinyl records, the same thing can be done: placing a finger on the turntable to give friction will retard it, while giving it a "spin" can advance it.
A pitch shifter is a sound effects unit that raises or lowers the pitch of an audio signal by a preset interval. For example, a pitch shifter set to increase the pitch by a fourth will raise each note three diatonic intervals above the notes actually played. Simple pitch shifters raise or lower the pitch by one or two octaves, while more sophisticated devices offer a range of interval alterations. Pitch shifters are included in most audio processors today.
A harmonizer is a type of pitch shifter that combines the pitch-shifted signal with the original to create a two or more note harmony.
In digital recording, pitch shifting is accomplished through digital signal processing. Older digital processors could often only shift pitch in post-production, whereas many modern devices using computer processing technology can change pitch values virtually in real time.
Pitch correction is a form of pitch shifting and is found in software such as Auto-Tune to correct intonation inaccuracies in a recording or performance. Pitch shifting may raise or lower all sounds in a recording by the same amount, whereas in practice, pitch correction may make different changes from note to note.
Numerous cartoons have used pitch shifters to produce distinctive animal voices. Alvin and the Chipmunks recordings with David Seville (aka Ross Bagdasarian) were created by recording vocal tracks at slow speeds, then playing them back at normal speeds. Voice artist Mel Blanc used pitch shifting techniques to create the voices of Tweety and Daffy Duck.
One notable early practitioner of pitch shifting in music is Chuck Berry, who used the technique to make his voice sound younger. Many of the Beatles' records from 1966 and 1967 were made by recording instrumental tracks a half-step higher and the vocals correspondingly low. Examples include "Rain", "I'm Only Sleeping", and "When I'm Sixty-Four".
The famous bass intro to the song "Seven Nation Army" by The White Stripes, is the result of guitarist Jack White playing a 6 string guitar through a pitch shifting effects pedal set to an octave below. The band was a duo, who lacked a bassist and had never previously used one in any of their music, choosing instead to mimic the sound of a bass guitar.