A  didgeridoo can be made of many materials aside from the natural eucalyptus trees hollowed out by termites in Northern Australia. Common materials include, but not limited to:  PVC, leather, glass, fiberglass, agave, yucca, and natural wood that has been split and "bored" out to be hollow.  The split method involves taking a fine piece of wood, like aspen or walnut, shaping it ahead of time to approximate size of the finished instrument, then cutting it in half with a band saw.  Once cut in half, each side is routed out with tools like a special wood carver called a Lancelot (looks kind of like a mini chain saw on a disc grinder).  Wood is then sanded inside, and meticulously glued back together using many hose clamps and special resin glues to hold the 2 halves back in their original shape, but now, of course, hollow inside.  The inside is sanded again with rods and sanding paper, along with the outside.  Both inside and outside are likely finished in a hard epoxy coating to add brightness to the finish and the to the tone of the didgeridoo.  How much is carved out on the inside, the taper and the thickness of the walls all determine the resulting sound of the instrument.  Agave and yucca are done in similar manner, but their sides are naturally quite thin, compared to wood, so epoxy is the general rule to give them strength and resonance.

Natural didgeridoos are a product of nature and man.  Termites (white ants to the native Australians) hollow out the inside of a living tree, notably a variety of the Eucalyptus tree family.  This generally occurs in the very northern and North Eastern part of Australia.  Skilled craftsmen can thump a tree and tell it's amount of hollow, and if it would be prudent to cut down or leave for later.  Once cut down the process is a matter of clearing out the inside of termite debris, machete off some of the outside wood to get down the the desired thickness and forming the bell end and mouthpiece. The instrument is then usually painted in special designs and artwork, generally unique to the artist/tribe.  Of the natural didgeridoos there are two main differences

Yirdaki - which are a longer and narrower bored instrument and are played in North East Arnhem Land (NEAL) with many rhythmical sound and overtone "toots" incorporated into the playing.  You will also see this referred to, at various sites and literature, as a Type B didgeridoo. 

Mago - Which tend to be a bit shorter, smooth walled on the inside and are more open all the way up the neck without too much undue narrowing in the neck to the mouthpiece.  They are played mostly in Western Arnhem Land (WAL) and have their own style of sounds and generally do NOT have the overtone toot of the Yirdaki.  You will also see this referenced to, at various sites and literature, as a Type A didgeridoo.

The sound of the didgeridoo is from the vibrating of the lips down the hollow tube and often combined with passive vocal "sound" and with deliberate vocal sounds imitating various animals like the bull frog, yelping dog, or bird sounds.  As far as any standard vocal sound there really isn't any that represents any particular didgeridoo note.  Some mouth sound are more notable as a "dup" and used over a wide area of playing.  This represents a sort of "spat" overtone.  In addition, rolling the tongue in the mouth sounds like a deep vocal growl from the didgeridoo.

"Dit-a-mo"- is a type of mouth sound from Western Arnhem Land, where the Mago is the preferred didgeridoo.  The "dit' is a forceful out-breath combined with a forecful tongue push that strike the upper palate just above the teeth.  The "a" part is a fast retraction of the tongue and an opening of the throat.  The "MO" has a low vocalized growl sound to it, known as Passive Vocals.  Another variant of WAL playing is "De-Ja-Ma", where the "De" is more forcefully accented, and the "Ma" is more subdued on the end.  All this done with rhythmical playing and usually incorporated as part of the circular breathing.  The didgeridoo is an extension of the players mouth cavity, throat and diaphram  movements, along with buzzing of the lips.  One instrument may sound entirely different played by another skilled didgeridoo player, simply because of physical traits.

In contemporary, or modern renditions, the didgeridoo is played with an almost "new-age" air to it, using vocals and other accents that are simply not there in the traditional playing.  Many CDs and recording are done in this style, and it lends itself to a wide assortment of accompaniments to songs.  A single key instrument, but with the help of interference harmonics of the voice it can produce some amazingly diverse sounds.  But, no matter the sounds, the basic drone is unmistakable in the sound of the overall instruments.

Also, you may find this musical instrument spelled didjeridoo, didjeridu, didje, didge, and even more unusual names arising from the individual tribes and clans of the Aboriginal People of Australia.