In this exhibit, you can raise and lower the pitch of your voice by more than one octave without changing the tempo. When you speak into the microphone you make the air around the microphone vibrate. An electronic circuit picks up the vibrations, changes the frequency, and then sends the result to the earphones. When you turn the pitch control higher, the circuit increases the frequency of the vibrations. When you turn the control lower, the circuit decreases the frequency of the vibrations. To raise the pitch of your voice by an octave, the circuit has to double the frequency of the vibrations you make.