Set up a microphone so that an instrument cable goes into a vocal or guitar effect, which will then be hooked up to an amplifier. One of the best ways to achieve a chipmunk voice is to speak through an Electro-Harmonix Poly Octave Generator 2 (POG 2), or a Digitech Whammy pedal. Other effects pedals can produce a similar sound as well.
Speak into the microphone and adjust the pitch of a POG 2 or Whammy pedal. With the POG 2, raise the slider of the +2 Octave all the way, and lower all others. With the Whammy, spin the knob until the 2 Octaves Up is selected.
Adjust the levels until the desired sound is achieved. For the POG 2, you can set the slider to higher or lower setting depending on how high-pitched you want the voice to be. The Whammy effect is not as adjustable as the POG 2, but can still get the job done if you select an octave or two higher.
Record the voice to a computer or looping effect for further sound engineering possibilities. For example, adding a vibrato effect at a fast rate of speed can make the voice sound exactly like a singing chipmunk. Reverb can be added as well to make you sound like you are performing in a concert hall.