1. Singing: the mechanism and the technic;Vennard,1967
2. Science session III;Ruhlman,1984
3. A model of frequency vibrato;Shipp,1984
4. Vocal vibrato/rate and extent of vibrato as a function of vowel, effort and frequency;Shipp,1979
5. Vibrato characteristics of tenors singing high C's;Keidar,1984