Singing involves the same organs as speaking: Diaphragm, lungs, the vocal folds with the vocal cords in the larynx and the vocal tract above the larynx. As in speech, the voice is produced in particular by the vibrating vocal cords, and the sound is formed primarily in the vocal tract. Numerous muscles cause a changing tension of the vocal folds.
The length of the vocal cords and their vibration behaviour are primarily responsible for the pitch of the voice. Children initially have a very high voice, which decreases as the vocal cords grow. This growth is much more pronounced in boys than in girls and a voice change marks the strongest growth phase.
Until the 18th century, and occasionally even until the beginning of the 20th century, there were castrati who retained their childlike high voice through an operation or mutilation, but had to pay for this with the loss of their procreative ability. Today, men with specially trained falsetto sing in comparable voice ranges as countertenors, altos, or sopranos. The faithful alternative of using boys' voices is also practised.
Singing with closed lips is called humming. The air is thereby completely discharged through the nose, which causes only a very small amount of air to vibrate.
The functioning of the human singing voice can be compared in a very simplified way with the padded pipes (cf. wind instruments and sound); the pads correspond to the two vocal folds, which are located opposite each other between the thyroid cartilage and two movable cartilages (which, together with the cricoid cartilage and the epiglottis, form the laryngeal skeleton) and are stretched out slightly inclined upwards towards each other.