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 stored 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.