The rhythm of the circular breathing, gives the instrument its readily recognizable sound. Other changes in the didgeridoo's sound can be made by adding vocal sounds to the drone. Most of the sounds are related to the sounds of Australian animals, such as the dingo or the kookaburra. To make these sounds, the players simply have to use their voice to make the sounds of the animals whilst continuing to blow air through the instrument. The results range from very high-pitched sounds to very low sounds. Adding vocal sounds increases the complexity of the playing.