The frame is held firmly against the performer's parted teeth or lips (depending on the type), using the jaw and mouth as a resonator, greatly increasing the volume of the instrument. The teeth must be parted sufficiently for the reed to vibrate freely, and the fleshy parts of the mouth should not come into contact with the reed to prevent damping of the vibrations and possible pain. The note or tone thus produced is constant in pitch, though by changing the shape of the mouth, and the amount of air contained in it (and in some traditions closing the glottis), the performer can cause different overtones to sound and thus create melodies.