Comment: Smoothing out the different vowels to make fast singing with words more easy.

Quote: Acoustically, each vowel is defined and resonated because of a special arrangement, concentration and distribution of energy within the overtone structures. When one conceptualizes a vowel, the appropriate muscle systems adjust the vocal tract (the trachea, the larynx, the laryngo- and oropharynges and the mouth) so that they energize certain frequencies while suppressing others. In this way it becomes possible to both "color" and resonate a great many vowel phonemes over an extensive pitch range. (Essays on the Nature of Singing)