Besides that quality which is peculiar to each individual, the voice may have several others, some of which, as purity, are due to the perfection of the entire vocal apparatus, and others, as the hoarse nasal or guttural quality, arise either from the unskil-fulness of the singer or from some change in the organ. There are two forms, however, remarkable because they may be produced at the will of the artist, these are the muffled voice and the clear voice. Their names indicate their nature. In the muffled, the sound is rounder, more velvety, and resembles less the sound of a reed; the pronunciation of the letters is less distinct and sharp, and the noisy vowels, like the a and e, incline to the timbre of o and u. In the clear voice the sound is piercing, somewhat noisy, and less agreeable to the ear. This high key is more common among the northern nations of Europe, while the graver one is ordinarily adopted by the singers of the south.
It is generally admitted that the muffled voice is caused principally by the immobility of the larynx when as low as possible, and in fact the larynx is usually in that position in singing in this tone: though M. Segond has occasionally seen the larynx as high as possible when this voice was produced. This voice seems to depend on the narrowing of the buccal orifice and the isthmus of the throat, coincident with as great a dilatation of the mouth as possible, a disposition which muffles and veils the resonance of the sound in the cavities of the pharynx and vocal tube. If in singing the letter a, with the mouth wide open, the lips be made slowly to approach each other, and pressing them together without extending them, the sound passes from the clear to the muffled tone, and the vowel a sounds like 0. This movement of the lips was very apparent in Mademoiselle Giulia Grisi in certain high notes, but even her admirable voice was insufficient to make us pardon her for thus marring features worthy the pencil of Raphael.