1. https://en.wikipedia.org/wiki/Human_voice
2. https://www.wyomingehdi.org/types-of-hearing-loss/
3. Rosenbaum, S., Simon, P.: Speech and Language Disorders in Children: Implications for the Social Security Administration's Supplemental Security Income Program. National Academies Press. 500 Fifth Street NW, Washington, DC 20001. (2016)
4. Hudgins, C.V.: A comparative study of the speech coordinations of deaf and normal subjects./. genet. Psychol. 44 ~ 3, 48. (1934)
5. Hudgins, C.V., Numbers, F.C.: An investigation of the intelligibility of the speech of the deaf. Genetic psychology monographs (1942)