A. Of the sounds cc (as in see), ay (as in say), B. Of the sounds oo (as in too), oh (as in go),e (as in met), ab (as in calm) a  a metallic, shrill tone. Such habits show wrong use of the resonating column of air. Correction may require extreme measures. By that is meant that a person whose voice is overly dark should practise bright vowel sounds until a proper balance and employment of the resonating cavities are established. If the voice is too brilliant, the darker vowels should be emphasized.

With normal voices all sounds should be used. However, both speaker and singer should learn to color each vowel in different ways so that quality of tone and meaning of words will agree. For example, it is necessary at times for the vowel ee to partake of a somber quality. This usually can be accomplished by rounding and protruding the lips, somewhat as you do in pronouncing the umlaut u (ii) in German. The vowel oo can be brightened to a considerable degree by slightly spreading the lips.

In classifying vowels, some seem naturally to have a less pleasant quality than others, as for example, those frequently heard in and, hand, at, air, hear, there, her, urge, are, war, far. Some people have no difficulty in pronouncing these sounds easily and pleasingly. Others produce them in such a way as to make the voice rough and unpleasant.

Listen to your own voice as you say and sing these sounds. Is the quality as agreeable and musical as it should be? If not, observe the position of your articulatory organs. Is your tongue raised very high toward the roof of your mouth, and are your lips spread tensely when you say at, can, man? When you say curl, war, fair, is the tip of your tongue inverted toward the roof of your mouth? If so, much of the unpleasantness will be eliminated if you keep the tip of the tongue near the inner surface of your lower teeth and relax your lips and jaw.

Vocal Release Singing Techniques