Fourth International Orca Symposium and Workshop - CEBC - CNRS

wide frequency response (up to 40 kHz or so) and good dynamic range. The Nagra IV is an
example of a quality, field-capable reel-to-reel recorder.
Most field researchers recording sounds of killer whales use Digital Audio Tape (DAT)
recorders, which provide sampling rates up to 48 kHz, or an audio bandwidth to 24 kHz. The
group recommended Sony models (e.g. D7, D8, D10 or D100) of DAT recorders. Tascam
also produces good DAT recorders, although they have no time/date indexing, which could be
a disadvantage in behavioural acoustic studies. Digital video recorders can record highquality
16-bit audio tracks comparable to DAT recordings, and have the advantage of
documenting concurrent surface behaviour of animals. However, most have Automatic Gain
Controls (AGCs) rather than manual record level controls, which are not well suited to the
loud, punctuated nature of killer whale clicks and calls. Mini-disc recorders are not
recommended for scientific recordings, since they involve a lossy compression algorithm,
which affects the accuracy of spectral analyses. Recording directly to hard disks on portable
computers can yield high quality data, though many laptops are not robust enough for use in
small boats in the marine environment. Larger ‘lunch-box’ style portable computers allow for
the use of high-speed signal processing cards, which can yield extremely wideband recordings
of echolocation clicks when used with appropriate broadband hydrophones.
For data archiving, it should be noted that analogue tape media (reel-to-reel and audio
cassette) are unlikely to survive more than 20-30 years. Many reel-to-reel tapes from the
1980s and earlier cannot be read today due to sloughing of the magnetic coating on the tapes.
Recordable CD and DVDs (CD-R and DVD-R) are expected to have a longevity of 50-75
years, so digital transfer to this medium may be useful for archiving data. Other options for
data archiving include contributing to institution-based acoustic archiving programs,
including those at the British Museum of Natural History and Cornell University.
In recent years, a variety of acoustic analysis software packages have become available
that are very useful for killer whale studies. CoolEdit 2000 is a popular and inexpensive
program that offers both spectrographic or waveform displays in real-time and a variety of
other functions. One limitation is its inability to print spectrograms. Another popular tool,
though far more expensive, is Avisoft-SASLab Pro, a program that is designed for
bioacoustical analysis. It produces excellent spectrogram hardcopies. Canary, a bioacoustical
software package from the Bioacoustical Research Program at Cornell University, is also
widely used. It lacks real-time browsing capability and runs only on Macintosh computers.
Other programs used in killer whale acoustic studies are Signal RTS, Spectralab, SeaWave
(University of Pavia, Italy), and various custom programs that run with Matlab (Mathworks
Inc.).
Describing and defining signal structure
Killer whales produce a wide variety of complex acoustic signals which can be difficult
to describe and define in terms of physical structure and potential function. Clicks are
thought to be emitted primarily for echolocation purposes, though their potential role in social
communication requires further study. Pulses – similar in structure to echolocation clicks –
are often produced at high repetition rates (typically 500 Hz to ≥ 2500 Hz) which give the
aural impression of a continuous tone. Spectrographically, these signals are resolved as a
series of sidebands at intervals equivalent to the pulse repetition frequency. Most killer whale
calls are composed of such rapidly produced pulses. Energy is not necessarily greatest in the
FOURTH INTERNATIONAL ORCA SYMPOSIUM AND WORKSHOPS
SEPTEMBER 23-28 2002, CEBC-CNRS, France
20