Predicting Achievable Fundamental Frequency Ranges in Vocalization Across Species.
Vocal folds are used as sound sources in various species, but it is unknown how vocal fold morphologies are optimized for different acoustic objectives. Here we identify two main variables affecting range of vocal fold vibration frequency, namely vocal fold elongation and tissue fiber stress. A simple vibrating string model is used to predict fundamental frequency ranges across species of different vocal fold sizes. While average fundamental frequency is predominantly determined by vocal fold length (larynx size), range of fundamental frequency is facilitated by (1) laryngeal muscles that control elongation and by (2) nonlinearity in tissue fiber tension. One adaptation that would increase fundamental frequency range is greater freedom in joint rotation or gliding of two cartilages (thyroid and cricoid), so that vocal fold length change is maximized. Alternatively, tissue layers can develop to bear a disproportionate fiber tension (i.e., a ligament with high density collagen fibers), increasing the fundamental frequency range and thereby vocal versatility. The range of fundamental frequency across species is thus not simply one-dimensional, but can be conceptualized as the dependent variable in a multi-dimensional morphospace. In humans, this could allow for variations that could be clinically important for voice therapy and vocal fold repair. Alternative solutions could also have importance in vocal training for singing and other highly-skilled vocalizations.
National Center for Voice and Speech, University of Utah, Salt Lake City, Utah, United States of America.
Ingo
I
Titze
National Center for Voice and Speech, University of Utah, Salt Lake City, Utah, United States of America.|Department of Physiology, Midwestern University, Glendale, Arizona, United States of America.
Tobias
T
Riede
Department of Otolaryngology-Head and Neck Surgery, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.
Ted
T
Mau
D000162:Acoustics; D000818:Animals; D019295:Computational Biology; D005260:Female; D006801:Humans; D007830:Larynx / Q000502:physiology; D008297:Male; D008954:Models, Biological; D013045:Species Specificity; D013061:Speech Acoustics; D014732:Vibration; D014827:Vocal Cords / Q000033:anatomy & histology / Q000502:physiology*; D014828:Vocalization, Animal / Q000502:physiology*