Didjeridu

The didjeridu (also known as a didgeridoo) is a wind instrument developed by indigenous Australians of northern Australia around 1,500 years ago and still in widespread use today both in Australia and around the world. It is sometimes described as a natural wooden trumpet or "drone pipe". Musicologists classify it as a brass aerophone.

A modern didjeridu is usually cylindrical or conical, and can measure anywhere from one to three meters long. Most are around 1.2 meters long. Generally, the longer the instrument, the lower the pitch or key of the instrument. However, flared instruments play a higher pitch than unflared instruments of the same length.

Construction
Authentic Aboriginal didjeridus are produced in traditionally oriented communities in Northern Australia or by makers who travel to Central and Northern Australia to collect the raw materials. They are usually made from hardwoods, especially the various eucalyptus species that are endemic to the region. Generally the main trunk of the tree is harvested, though a substantial branch may be used instead. Aboriginal didjeridu craftsmen hunt for suitably hollow live trees in areas with obvious termite activity. Termites attack these living eucalyptus trees, removing only the dead heartwood of the tree, as the living sapwood contains a chemical that repels the insects. Various techniques are employed to find trees with a suitable hollow, including knowledge of landscape and termite activity patterns, and a kind of tap or knock test, in which the bark of the tree is peeled back, and a fingernail or the blunt end of a tool, such as an axe is knocked against the wood to determine if the hollow produces the right resonance.

Once a suitably hollow tree is found, it is cut down and cleaned out, the bark is taken off, the ends trimmed, and the exterior is shaped; this results in a finished instrument. This instrument may be painted or left undecorated. A rim of beeswax may be applied to the mouthpiece end. Traditional instruments made by Aboriginal craftsmen in Arnhem Land are sometimes fitted with a 'sugarbag' mouthpiece. This black beeswax comes from wild bees and has a distinctive aroma.

Non-traditional didjeridus can also be made from PVC piping, non-native hard woods (typically split, hollowed and rejoined), glass, fiberglass, metal, agave, clay, hemp (in the form of a bioplastic named zelfo), and even carbon fibre. These didges typically have an upper inside diameter of around 1.25" down to a bell end of anywhere between two to eight inches and have a length corresponding to the desired key. The mouthpiece can be constructed of beeswax, hardwood or simply sanded and sized by the craftsman. In PVC, an appropriately sized rubber stopper with a hole cut into it is equally acceptable, or to finely sand and buff the end of the pipe to create a comfortable mouthpiece.

Modern didjeridu designs are distinct from the traditional Australian Aboriginal didjeridu, and are innovations recognized by musicologists. Didjeridu design innovation started in the late 20th Century using non-traditional materials and non-traditional shapes.

Playing the Didjeridu
The didjeridu 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 whilst simultaneously expelling stored 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. Recordings exist of modern didgeridoo players playing continuously for more than 40 minutes; Mark Atkins on Didgeridoo Concerto (1994) plays for over 50 minutes continuously.

Fellow of the British Society Anthony Baines wrote that the didjeridu functions "...as an aural kaleidoscope of timbres" and that "the extremely difficult virtuoso techniques developed by expert performers find no parallel elsewhere."

More modern approaches to playing the didjeridu are starting to show up in performances and lessons around the World. One of these techniques involves combining beatboxing with playing the didgeridoo. It was featured on the British children's TV series Blue Peter.

Physics and operation
A termite-bored didjeridu has an irregular shape that, overall, usually increases in diameter towards the lower end. This shape means that its resonances occur at frequencies that are not harmonically spaced in frequency. This contrasts with the harmonic spacing of the resonances in a cylindrical plastic pipe, whose resonant frequencies fall in the ratio 1:3:5 etc. The second resonance of a didjeridu (the note sounded by overblowing) 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 didjeridu's sound can be made by adding vocalizations to the drone. Most of the vocalizations are related to sounds emitted by Australian animals, such as the dingo or the kookaburra. To produce these sounds, the players simply have to use their vocal cords to produce the sounds of the animals whilst continuing to blow air through the instrument. The results range from very high-pitched sounds to much lower guttural vibrations. Adding vocalizations increases the complexity of the playing.

Use in film music

 * Jerry Goldsmith used the didjeridu in his 1979 score for the Ridley Scott science-fiction horror film Alien, lending a noisome and grotesque air to the presentation of the alien creature in its different forms: first as the "facehugger" (the opening phrases of "Hanging On"), and later as the full-grown beast (in "Out the Door").
 * The didjeridu made a brief appearance in the first of George Lucas's prequel films, Star Wars Episode I: The Phantom Menace, filling in for the Gungan horn call before the Battle of Naboo begins.