are collectively known as the 'low' or 'chalumeau' register. By increasing breath pressure and opening a small hole high up on the tube using a special 'register key', the clarinet can be caused to 'overblow'. The air in the tube switches to a different type of resonance and all the notes go up in pitch by an octave and a half. These new notes are collectively known as the 'middle' or 'clarino' register. By complicated fingering and a further increase in breath pressure, another shift can be produced into the 'high' or 'altissimo' register.