Editing Didgeridoo (section)

== Physics and operation ==
{{further|Frequency spectrum}}
[[File:Didgeridoo street player-2.jpg|thumb|Didgeridoo street player in Spain]]

A termite-bored didgeridoo 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 didgeridoo (the note sounded by overblowing) is usually around an [[eleventh|11th]] higher than the fundamental frequency (a frequency ratio of 8:3).

The vibration produced by the player's lips has harmonics 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's resonances, as is usually the case for Western wind instruments (e.g., in the low range of the [[clarinet]], the 1st, 3rd, and 5th harmonics of the reed are assisted by resonances of the bore).

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 recognisable sound.<ref>Tarnopolsky, A, Fletcher, N. Hollenberg, L., Lange, B., Smith, J. and Wolfe, J. (2006)"Vocal tract resonances and the sound of the Australian didjeridu (yidaki) I: Experiment", J. Acoust. Soc. America, 119, 1194-1204. https://www.phys.unsw.edu.au/~jw/reprints/Tarnopolskyetal.pdf</ref><ref>{{Cite web|title=Didgeridoo acoustics/ yidaki acoustics/ didjeridu acoustics|url=https://www.phys.unsw.edu.au/jw/didjeridu.html|access-date=18 February 2023|publisher=University of New South Wales
| last = Wolfe | first = Joe}}</ref>

Other variations in the didgeridoo's sound can be made by adding vocalisations to the drone. Most of the vocalisations are related to sounds emitted by Australian animals, such as the [[dingo]] or the [[kookaburra]]. To produce these sounds, the players use their vocal folds 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 sounds involving interference between the lip and vocal fold vibrations.<ref>Wolfe, J. and Smith, J. (2008) "Acoustical coupling between lip valves and vocal folds", Acoustics Australia, 36, 23-27. https://newt.phys.unsw.edu.au/jw/reprints/WolfeSmithAA.pdf</ref>  Adding vocalisations increases the complexity of the playing.