Harmonizer

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" or "pitch benders".

The simplest methods are used to increase pitch and reduce durations, or vice versa, 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 drive shaft, or using a different motor. As technologies improved later designs of 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 turnable 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 "shifted" pitch with the original pitch to create a two or more note harmony.

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Wikipedia