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Energy distribution in pulsed vocalizations

Subject: Energy distribution in pulsed vocalizations
From: Harald Yurk <>
Date: Wed, 31 Jul 2002 13:29:53 -0700
Dear List Members 
 I am studying the behavioral use of pulsed vocalizations by killer whales.
 As many of you know those cetaceans produce discrete calls that can be
 easily recognized by their spectrographical side band structure of their
 pulsed vocalizations.
 When calls are recorded with a single hydrophone, the greatest energy
 measured from the spectrogram can be found on either one of those side
 bands. As I understand it, those side bands are produced by an artifact of
 the spectrographical analysis because a Fast-Fourier-Transformation always
 assumes the existence of harmonics. The side bands, however reflect the
 pulse repetition rate of pulsed signals (Watkins 1966). What I am curious
 about and don't really understand, is why the highest energy is not always
 found on the same side band. Are other physical conditions outside of the
 sound producing whale responsible for those differences, or does body
 movement affect the energy to shift between sidebands or .. ?
 Maybe someone with better understanding of physical acoustics than myself
 can help with this. Thank you very much.
 Best regards,
 Harald Yurk
 Department of Zoology
 Marine Mammal Research Unit
 University of British Columbia
 6270 University Boulevard
 Vancouver, B.C., Canada V6T 1Z4
 Phone:(604) 822-8181
 Fax:(604) 822-8180

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