Overpressure (winds)

Overpressure on wind instruments is a very common device for achieving aggressive, dense sounds. It can also be used to produce sounds rich in harmonics.

The image shows a transition from ordinary pressure (empty rectangle) to overpressure (filled rectangle). Overpressure can be produced in different ways, whether with the embouchure, the reed, or the instrument itself. Examples of this technique, controlled on clarinet, can be heard at this link.