Dear List Members,
I just wanted to thank everyone who replied to my question. To summarize;
Dave Mellinger and William O'Neill both provided good explanations for
differences in energy distribution of spectrographic side bands of the same
pulsed vocalization. Both referred to physical phenomena that could affect
the relative intensity of various side bands, such as bottom and surface
reflection, depth of the vocalizing whale relative to the depth of the
hydrophone.
Furthermore, Dave, William, Magnus Wahlberg and Scott Murray pointed out
that pulses have a temporal extension and thereby are in fact damped
oscillations with a pulse tone frequency. The pulse rate, which can be
controlled by the whale could have an influence on the relative strength of
side bands, either constructive or destructive, depending on whether the
pulse repetition rate is great enough to produce overlaps of single pulses.
Many thanks to everyone, especially to Dave for the Bradbury and Vehrenkamp
reference. The book was already sitting on my desk and is indeed very useful
for the understanding of those phenomena.
Best regards,
Harald
P.S. For those of you interested in killer whale calls. Our work on Alaskan
resident killer whale calls has just been published in the latest issue of
Animal Behaviour
*****************************************************
Harald Yurk
Department of Zoology Vancouver Aquarium Marine Science Centre
University of British Columbia In Stanley Park, P.O. Box 3232
6270 University Boulevard Vancouver, B.C., Canada V6B 3X8
Vancouver, B.C., Canada V6T 1Z4 Phone: (604) 6593429/3428/3430
Phone:(604) 822-8181
Fax:(604) 822-8180
> From: Harald Yurk <[EMAIL PROTECTED]>
> Reply-To: [EMAIL PROTECTED]
> Date: Tue, 30 Jul 2002 15:03:23 -0700
> To: <[EMAIL PROTECTED]>
> Subject: Energy distribution in pulsed vocalizations
>
> 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
>
> *****************************************************
> 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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