We frequently hear agreeable tones, as far as musical quality is concerned, but we have, in nine such cases out of ten, to dispense with a clearly defined vowel, as, in order to obtain the musical quality, the singer generally sacrifices, or distorts, the vowel, so that it might be anything but that which it is in tended to be.

This fault has been tacitly encouraged by many teachers, owing, I think, to attention having been called by laryngoscopists to the change which takes place in the shape of the vowel forms, to reenforce properly the different pitches of tone. A misunderstanding of this theory in its practical application has been made an excuse for slovenly pronunciation. To alter or distort the sound of the vowel in order to favor the resonance of the tone is working quite in the wrong direction, — it is robbing Peter to pay Paul.

The theory of altered vowels would not, however, have worked the harm it has done if it had been accompanied with the counterbalancing law that, what ever physiological changes may have to take place to furnish a resonant and musical sound on certain combinations of pitch and vowel, the clearness and distinctness of the vowel sound to the ear must at all costs be maintained.

Rogers, Clara Kathleen. My Voice and I: Or, The Relation of the Singer to the Song. AC McClurg & Company, 1910.