CHOOSING A DIDGERIDOO

Sound

Of course, a very important feature of the didgeridoo will be its sound. This can be quite subjective, depending on the personal tastes of each person. However, the sound of a good didgeridoo should generally have a few characteristics you should be looking for.
First, test the didgeridoo by playing it. If you play while your didgeridoo is on a hard surface and facing a hard wall, it will reflect some of the sound back to you, allowing you to hear it more clearly.
Listen to the quality of your basic drone. Then try some of the techniques mentioned in the previous section on playability. Alternate between playing with your cheeks in or out, and move your tongue back and forth as you drone. Listen carefully to how your didgeridoo sounds.
If the sounds of the didgeridoo are muffled, soft, dull or 'hollow', and you can't hear much variation in sound as you try different techniques, the sound quality of the didgeridoo may not be so good and you might want to try another didgeridoo.
If your didgeridoo sounds reasonably loud, clear, sharp and bright, and it offers a basic range of different sounds, then this should be a good didgeridoo to consider, as long as it meets the other important criteria such as playability and backpressure.
If you are having trouble listening to your didgeridoo as you play, try to get someone else to play for you, and stand facing the bell end. Have a good listen over a couple of minutes to determine whether the sound appeals to you.

Key

Didgeridoos have a single pitch, or key, mainly determined by the length and internal dimensions of the instrument. Most well made didgeridoos are tuned professionally by the maker, so they can be played in harmony with other instruments.
Commonly available didgeridoos generally fall within the range of C to F, although they can go higher or lower. Longer or wide bored didgeridoos (with a large volume within the chamber) play in a low key, while shorter or narrow bore didgeridoos (with a smaller volume) play in a higher key.
Lower key didgeridoos, with the greater volume of air inside the didge, require more air to be blown into the didgeridoo for the lips to vibrate. This contributes to a lower backpressure didgeridoo.
Different keys have certain characteristics that will suit different players. Those looking to play low, earthy, bassy drones in a slow and meditative way will prefer the lower, warmer drone of the lower keyed, C or D didges.
Those wishing to play sharper, snappier rhythms will prefer the bright, crisp drones of the higher, E or F didges. Those looking for didges in the mid-range will enjoy D didges for their diversity.  D, E or F didges are best for beginners to learn on, as they offer best playability. See the chart and listen to the audio files below for a better understanding of didgeridoo keys.

Chart showing the relationship of commonly available didgeridoo keys to the sound of the drone and the capability for playing fast rhythms.

							G
						F
					E
				D
			C
		B

This relates to the chart above. Click on the buttons to hear how the pitch and playing speed is affected by the key (indicative).
Higher key didgeridoos have less volume of air inside them, so they don't require as much air to be blown into it to play. This creates a higher backpressure didgeridoo.
Because higher key didges require less air to play and generally have good backpressure, they are good to start out on, and are easier for learning circular breathing where conserving your air is most important.
Advanced players will make great sounds on any didgeridoo, although they would also tend towards the higher keyed E, F or G didges if they are looking to play fast, complex rhythms. Lower keyed didges, while great for making powerful, rumbling, meditative drones, are not conducive for fast, intricate playing.
Personally, I enjoy playing higher keyed didgeridoos because they allow me to play faster rhythms. I started playing with a D key didgeridoo, but eventually moved to highger key didgeridoos when I wanted to play more advanced rhythms. I also like the higher pitch of the E and F didgeridoos and the level of energy it offers. These higher keys also have the ability to cut through distracting noises when you are playing for an audience and have a lot of impact. I also find E and F didgeridoos to offer the most diverse range of sounds.