A pitch shifter (also called an "octaver" for effects that shift pitch by an octave) raises or lowers (e.g. "transposes") each note a performer plays by a pre-set interval. For example, a pitch shifter set to increase the pitch by a fourth will raise each note four 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. A pitch shifter can be used by an electric guitarist to play notes that would normally only be available on an electric bass. As well, a bass player with a four string electric bass can use an octave pedal to obtain low notes that would normally only be obtainable with a five-string bass with a low "B" string.
A harmonizer is a type of pitch shifter that combines the altered pitch with the original pitch to create a two or more note harmony. Some hamonizers are able to create chorus-like effects by adding very tiny shifts in pitch.