Some believe didgeridoos are the world's oldest wind instrument, dating back as far as 20,000 BC. Archaeological studies of rock art in Northern Australia suggests that the Aboriginal people of the Kakadu region of the Northern Territory have been using the didgeridoo for about 1500 years, based on the dating of paintings on cave walls and shelters from this period. A clear rock painting in Ginga Wardelirrhmeng from the freshwater period (1500 years ago until the present).
The didgeridoo is sometimes described as a natural wooden trumpet or "drone pipe". Musicologists classify it as an aerophone. Didgeridoos are part of the musical, healing and ceremonial heritage of the aboriginal peoples of Australia. Traditional playing of the didgeridoo is accompanied by tapping out soft rhythms on the sides of the instrument while it is being played. Louder rhythms can be achieved by clapping sticks together. According to one rendition of an aboriginal legend, the first man wanted to please the sky. He put a hollowed branch to his mouth and began to play. With the force of his breath, the termites living in the hollow branch were expelled from the open end and became the stars.
The Aborigines made their didgeridoos eucalyptus branches. There are hundreds of eucalyptus species, but only a few are used to make the didgeridoo. The eucalyptus grows with a fleshy center. If any insect or animal makes a small hold in the outer bark of the branch, termites move in. It takes about a year for them to hollow out the branch or sapling leaving the dense outer part of the eucalyptus intact. Didgeridoos are now made from a number of natural and synthetic materials.
A modern didgeridoo is usually cylindrical or conical in shape and can measure anywhere from 1 to 3 m (3.2 ft to 9.8 ft) in length with most instruments measuring around 1.2 metres (3.9 ft). The length is directly related to the 1/2 sound wavelength of the keynote. Generally, the longer the instrument, the lower the pitch or key of the instrument. Keys from D to F sharp are the preferred pitch of traditional Aboriginal players.
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 whilst 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. 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.
A 2005 study in the British Medical Journal found that learning and practising the didgeridoo helped reduce snoring and sleep apnea, as well as daytime sleepiness. This appears to work by strengthening muscles in the upper airway, thus reducing their tendency to collapse during sleep. According to the study "four months of training of the upper airways by didgeridoo playing reduces daytime sleepiness in people with snoring and obstructive sleep apnoea syndrome. The reduction of the apnoea-hypopnoea index by didgeridoo playing indicated that the collapsibility of the upper airways decreased. In addition, the partners of participants in the didgeridoo group were much less disturbed in their sleep."