Technique used by woodwind players to ascend to a higher register. The Air column of a woodwind instrument is characterized by a set of natural (‘normal’) modes of vibration. A stable note can normally be sounded only if its fundamental frequency is close to that of one of the natural modes (or resonances) of the air column (see Acoustics, §IV). In the first register of an instrument, the fundamental frequency of the sounded note is close to the first natural mode frequency; within this register, the pitch is changed by altering the pattern of open and closed side holes (see Fingering, §III), thereby modifying the length of the air column and hence the first mode frequency. Overblowing is the term applied to the process by which the player ascends to a higher register, in which the fundamental frequency of the sounded note is close to the frequency of the second (or a higher) air column mode.
For instruments with approximately conical tubes (such as the oboe or bassoon), and for those with approximately cylindrical tubes effectively open at both ends (such as the flute), the frequencies of the first few natural modes form a complete harmonic series (frequency ratios 1:2:3 …); these instruments therefore overblow to the octave in the second register. For cylindrical instruments effectively closed at one end (such as the clarinet), the lower natural mode frequencies form an odd-member-only harmonic series (frequency ratios 1:3:5 …), and these instruments overblow to the 12th.
On the flute overblowing involves an increase in blowing pressure, modification of the shape of the jet of air issuing from the lips, and the angle at which this strikes the far edge of the mouth-hole. On a reed instrument it requires, as well as increased wind pressure, the adjustment of the pressure and position of the lips on the reed blade. Modern reed instruments have certain very small ‘speaker’ holes in the body tube which assist the process (see Speaker key). The muscular adjustments required are extremely small and subtle, and are learnt only by long and assiduous practice. Once acquired, however, they become quite automatic to the player.
PHILIP BATE/MURRAY CAMPBELL