A talk box is an effects unit that allows musicians to modify the sound of a musical instrument by shaping the frequency content of the sound and to apply speech sounds onto the sounds of the instrument. Typically, a talk box directs sound from the instrument into the musician's mouth by means of a plastic tube adjacent to a vocal microphone. The musician controls the modification of the instrument's sound by changing the shape of the mouth, "vocalizing" the instrument's output into a microphone.