It is impossible to sing well when mentally depressed or even physically indisposed slightly. Unless one has complete control over the entire vocal apparatus and unless one can simulate a smile one does not feel the voice will lack some of its resonant quality, particularly in the upper notes, where the smiling position of the mouth adjusts the throat and air passages for the emission of light tones.
The lips are of the greatest aid in shaping and shading the tones. Wagnerian singers, for instance, who employ trumpet-like notes in certain passages are often seen shaping their lips like the mouthpiece of a trumpet, with a somewhat square opening, the lips protruding.
However, this can be practiced only after perfect relaxation of the jaw and control of the tongue have been accomplished.
A singer's mouth must always look pleasant, not only because it creates a disagreeable impression on the audience to see a crooked and contorted mouth, but also because natural and correct voice production requires a mouth shaped almost into a smile.
Too wide a smile often accompanies what is called "the white voice." This is a voice production where a head resonance alone is employed, without sufficient of the apoggio or enough of the mouth resonance to give the tone a vital quality. This "white voice" should be thoroughly understood and is one of the many shades of tone a singer can use at times, just as the impressionist uses various unusual colors to produce certain atmospheric effects.
For instance, in the mad scene in "Lucia" the use of the "white voice" suggests the babbling of the mad woman, as the same voice in the last act of "Traviata" or in the last act of "Bohème" suggests utter physical exhaustion and the approach of death.
An entire voice production on these colorless lines, however, would always lack the brilliancy and the vitality which inspire enthusiasm.
One of the compensations of the "white voice" singer is the fact that she usually possesses a perfect diction. The voice itself is thrust into the head cavities and not allowed to vibrate in the face and mouth and gives ample room for the formation of vowels and consonants. And the singer with this voice production usually concentrates her entire attention on diction.
The cure for this tone emission is, first of all, the cultivation of the breath prop, then attacking the vowel sound o o in the medium voice, which requires a low position of the larynx, and exercises on the ascending scale until the higher notes have been brought down, as it were, and gain some of the body and support of the lower notes without losing their quality.
The singer's expression must concern itself chiefly with the play of emotion around the eyes, eyebrows and forehead. You have no idea how much expression you can get out of your eyebrows, for instance, until you study the question and learn by experiment that a complete emotional scale can be symbolized outwardly in the movements of the eyelids and eyebrows.