The sound of the human voice is largely driven by the vibration of the vocal cords -- parallel bands of cartilage in the throat. This vibration creates sounds with a dominant pitch, or fundamental frequency, along with secondary pitches (or harmonics) of higher frequencies. In normal speech and singing, these harmonics are significantly weaker in force than the fundamental frequency, and are heard only as distinctions in timbre (such as the differences between two different people singing the same note). In Tuvan throat singing, however, singers manipulate their voices so that one of the harmonics is prominent enough to be heard as a distinct, whistle-like note on top of the primary pitch.
To create the characteristic prominent harmonics, Tuvan throat singers manipulate their vocal cords and other speech organs to amplify desired harmonics while reducing the intensity of others. In singing and speaking, the vocal cords vibrate by rapidly closing (touching each other) and opening as air from the lungs passes between them through the windpipe. In Tuvan throat singing, singers hold the vocal cords closed for a longer time, and open for a shorter time, during the vibrations.
To create melodies with harmonics, Tuvan throat singers move their tongues as they sing to adjust the pitches of the harmonics. Singers manipulate their tongues in different ways in different styles of Tuvan throat singing to create distinctive acoustic effects. This tongue manipulation occurs while the singers are also controlling their vocal cord vibrations.
Another strategy Tuvan throat singers use to amplify some harmonics while reducing the effect of extraneous frequencies is to sing with their jaws thrust forward and the lips protruded. This strategy preserves acoustic energy in the vocal tract, which amplifies desired frequencies without requiring any extra work from the vocal cords.