Most woodwind instruments have a second register that begins an octave above the first (with notes at twice the frequency of the lower notes). With the aid of an 'octave' or 'register' key, the notes sound an octave higher as the fingering pattern repeats. These instruments are said to overblow at the octave. The clarinet differs, since it acts as a closed-pipe system. The low chalumeau register plays fundamentals, but the clarion (second) register plays the third harmonics, a perfect twelfth higher than the fundamentals. The clarinet is therefore said to overblow at the twelfth. The first several notes of the altissimo (third) range, aided by the register key and venting with the first left-hand hole, play the fifth harmonics, a perfect twelfth plus a major sixth above the fundamentals. The fifth and seventh harmonics are also available, sounding a further sixth and fourth (a flat, diminished fifth) higher respectively; these are the notes of the altissimo register.
Most woodwind instruments have a second register that begins an octave above the first (with notes at twice the frequency of the lower notes). With the aid of an 'octave' or 'register' key, the notes sound an octave higher as the fingering pattern repeats. These instruments are said to overblow at the octave. The clarinet differs, since it acts as a closed-pipe system. The low chalumeau register plays fundamentals, but the clarion (second) register plays the third harmonics, a perfect twelfth higher than the fundamentals The clarinet is therefore said to overblow at the twelfth. The first several notes of the altissimo (third) range, aided by the register key and venting with the first left-hand hole, play the fifth harmonics, a perfect twelfth plus a major sixth above the fundamentals. The fifth and seventh harmonics are also available, sounding a further sixth and fourth (a flat, diminished fi.fth) higher respectively; these are the notes of the altissimo register.