A pitchshifter is an electronic device for changing the frequency of an audio signal without changing the timing characteristics.
It is common knowledge for example that you can take a given audio sample and play it at double speed, and the frequencies will all be twice as high, but the duration of the sample will also be half the original.
A pitch shifter allows the frequency of the signal to be altered while keeping the duration of the sample constant.
How is this possible? I don't exactly know, but I know it's possible because I have one of these devices. The one I have is called a Digitech Whammy Pedal and is generally used by guitar players for a variety of pitch shifting effects.
I've played my stereo through this thing, just to see how well it works. It works best with small changes in pitch. Large changes tend to introduce quite a lot of audible and not necessarily pleasant distortion into the signal, especially an arbitrary (non-guitar) signal such as that from a stereo. Changes of exactly an octave up or down are pretty good though.
Some of the settings on the Whammy Pedal:
Harmony: Pedal up Pedal Down:
Original signal + down 1 octave up 1 octave
down 5th down 4th
down 4th down 3rd
up 5th up 7th
up 5th up 6th
up 4th up 5th
up 3rd up 4th
up b3rd up 3rd
up 2nd up 3rd
original signal down 2 octaves
original signal down 1 octave
original signal down 2nd
original signal up 2 octaves
origianl signal up 1 octave
Detune: ("shallow" or "deep")
The unit has a "bypass" switch, a high impedance
phono-plug input for guitar, and 'wet" (with effect)
and "dry" (without effect) outputs.
The power supply required is 9V, 780mA AC (NOT DC)