mcbem-2014-01-submission-wwf-en

Amplitude
Table A1. The speed of sound (m/s) in various media, from JASCO Applied Sciences (2009).
Medium
Speed of sound in m/s
Air at 20 o C 343
Salt water at 25 o C 1532
Sand 800-2,200
Clay 1,000-2,500
Sandstone 1,400-4,300
Granite 5,500-5,900
Limestone 5,900-6,100
How do we describe sound?
Laypeople typically describe a sound by its loudness, and sometimes its pitch. The criteria that
determine these characteristics are basically the sound wave’s amplitude (loudness), frequency (pitch),
and duration. Waveforms are used to show time vs. amplitude (Figures A1-2), and spectrograms show
time vs frequency, much like a musical score (Figure A3). Continuous sounds such as boat noise are
described as chronic or non-pulsed whereas sounds that are of short duration, such as an explosion, or
of repeated short durations, such as pile driving or airgun firing, are pulsed (or acute, intermittent or
transient) sources of noise. In the Atlantic Ocean, airgun firing is such a predominant sound that it is
often described as chronic because it is ever-present, but the original signal is a pulsed sound. Sounds
such as killer whale whistles or military sonars are generally described as narrowband, whereas sounds
that encompass a range of frequencies, such as shipping noise or pile driving, are broadband (Figure A3).
1
0.5
a) Low frequency: 3 cycles/s (Hz) b) higher frequency: 6 cycles/s (Hz)
1
0.5
0
0
-0.5
-0.5
-1
-1
0 1 0 1
Time (s)
Figure A1. Waveforms of a low (a) and higher (b) frequency continuous sound wave.
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