Didgeridoo
Aboriginal instrument
The didgeridoo (also known as a didjeridu or didge) is a wind instrument of the
indigenous Australians of northern Australia. The instrument is traditionally
made from living Eucalyptus trees which have been hollowed out by termites.
Playing
The didgeridoo is played with continuously vibrating lips to produce the drone
while using a special breathing technique called circular breathing. This
requires breathing in through the nose while simultaneously expelling air out of
the mouth using the tongue and cheeks. By use of this technique, a skilled
player can replenish the air in their lungs and with practice can sustain a note
for as long as desired.
Physics and operation
A termite-bored didgeridoo has an irregular shape that usually increases in
diameter towards the lower end. This shape means that its resonances occur at
frequencies that are not harmonically spaced in frequency. The second resonance
of a didgeridoo (the note sounded by over-blowing) is usually around an 11th
higher than the fundamental frequency (a frequency ratio somewhat less than
3:1). The vibration produced by the player's lips has harmonics, i.e., it has
frequency components falling exactly in the ratio 1:2:3 etc. However, the
non-harmonic spacing of the instrument's resonances means that the harmonics of
the fundamental note are not systematically assisted by instrument resonances,
as is usually the case for Western wind instruments (e.g., in a clarinet, the
1st 3rd and 5th harmonics of the reed are assisted by resonances of the bore, at
least for notes in the low range). Sufficiently strong resonances of the vocal
tract can strongly influence the timbre of the instrument. At some frequencies,
whose values depend on the position of the player's tongue, resonances of the
vocal tract inhibit the oscillatory flow of air into the instrument. Bands of
frequencies that are not thus inhibited produce formants in the output sound.
These formants, and especially their variation during the inhalation and
exhalation phases of circular breathing, give the instrument its readily
recognizable sound. Other variations in the didgeridoo's sound can be made with
"screeches". Most of the "screeches" are related to sounds emitted by Australian
animals, such as the dingo or the kookaburra. To produce these "screeches", the
player simply has to cry out (into the didgeridoo) while continuing to blow air
through it. The results range from very high-pitched sounds to much lower
guttural vibrations.
