1. Abramson, A. S. 1975. Pitch in the perception of voicing states in Thai: Diachronic implications. Haskins Laboratories Status Reports on Speech Research, SR-41, 165–174.
2. Atkinson, J. E. 1973. Aspects of intonation in speech: Implications from an experimental study of fundamental frequency. Unpublished Ph.D. dissertation, Univ. of Connecticut.
3. Ballard, W. L. 1975. Wu tone sandhi. Paper presented at the 8th International Conference on Sino-Tibetan Languages and Linguistics, Berkeley.
4. Beach, D. M. 1938. The phonetics of the Hottentot language. Cambridge.
5. Frequency analysis of vowels produced in helium-rich atmosphere;Beil;Journal of the Acoustical Society of America,1962