When they're activated, they move the pitch of all the notes you play up an octave (12 frets), which can sound really cool if used correctly. So, they are exactly what they say on the tin.
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They can shift the pitch of what's coming from your guitar up or down.

An octave pedal would move up or down octaves.

Also called a pitch-shifter.
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A pitch shifter is an audio processor that changes the pitch of an audio signal.

The Digitech Whammy IV is an octave shifter but it has the ability to change pitch in different ways.
Last edited by 100%guitarmad at Feb 24, 2009,
They raise or lower your output by one, or many octaves and they can can layer many different octaves over your output. I'm sure youtube's got some nice videos of them.
youtube the electro harmonix pog (poly octave generator)
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