Vocal Faults by James C McKinney
I recommend this book for any teacher or student of singing as it not only diagnoses vocal faults, but also gives wonderful advice on breathing and support.
Not only identifying vocal problems, but the nature of vocal sound. The mechanism of the larynx etc. It also explains 'the register' of one's voice. The modal voice register, the falsetto register and the whistle register.
The nature of resonators, the vocal resonators, and faults relating to resonation.
The articulatory process, and establishing good articulatory habits.
A rationale for voice classification, and criteria for the establishment of voice classification.
