The quality of the human voice depends on the same laws as those determining the quality, klang-tint, or timbre of the tones produced by any musical instrument. Tones of a mixed character, that is to say, composed of a fundamental and partials, are produced by the vibrations of the true vocal cords, and certain of those partials are strengthened by the resonance of the air in the air-passages, and in the pharyngeal and oral cavities.
So strongly may certain of these partials be reinforced, as to obscure or hide the fundamental tone, and give a peculiar character to the sound. These, however, are only general statements, and there are still many difficulties in the way of a true interpretation of voice-tones. In the first place, we observe that we may sing a scale, using one sound for each note, such as la, la, la, etc. Or, by putting the mouth in a certain position, we can pronounce the so-called vowels, a, e, i, o, u (ou as the u in prune), uttering the sounds ah, ā, ē, o, ou. As we do so, we notice that each sound appears to the ear to have a pitch of its own, different from that of the others.