Volodin, I., Volodina, E., Frey, R., Carranza, J. & Torres-Porras, J. (2013). Spectrographic analysis points to source-filter coupling in rutting roars of Iberian red deer. Acta Ethol. 16, 57-63. DOI 10.1007/s10211-012-0133-1.
Source filter coupling is the rarest acoustic phenomenon not only in Iberian red deer, but in any mammal. In most mammals, sound production can be well described in the framework of source filter theory. The vocal output is the result of combined work of the larynx (the source) and of the supralaryngeal vocal tract (the filter). The source filter theory suggests the independence of sour ce and filter. Thus, vocal tractfiltering should not affect the fundamental frequency (f0) of the sound created in the larynx. Spectrographically, the source is mostly characterized by the f0 an ditsharmonics,whilethefilter
by the vocal tract resonances, i.e., formant frequencies. Nevertheless, a non-independent (coupled) source and filter can be proposed when the vocal folds start oscillating at one of the formant frequencies. Couplin gbetweensourceandfilterhas been found in human singers and predicted for red deer Cervus elaphus by a computer modeling approach. This study describes different modes of phonation in a natural bout of rutting calls of Iberian red deer Cervus elaphus hispanicus and the transition from a chaotic mode to a probable source
filter coupling mode. This ph enomenon might be involved in the production of extremely high-frequency bugles of North American and Asian subspecies of C. elaphus
https://link.springer.com/content/pdf/10.1007%2Fs10211-012-0133-1.pdf