In singing, air pressure from the lungs is used to set the vocal folds into periodic oscillation producing a pitched sound source at the base of the vocal tract. By changing the positions of the jaw, lips and tongue the resonances of the air in the vocal tract, called vocal formants, can be altered. We perceive the different tone qualities produced as the vowel sounds used in everyday communication. Vocal tract resonances can also be used to help explain how the trained singer can be heard over the sound of an entire orchestra.