A talk box or talkbox is an effects unit that allows musicians to modify the sound of a musical instrument. The effect can be used to shape the frequency content of the sound and to apply speech sounds (in the same way as singing) onto a musical instrument, typically a guitar (its non-guitar use is often confused with the vocoder) and keyboards. Typically, a talk box directs sound from an instrument into the musician's mouth by means of plastic tube adjacent to their 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.