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Transforming the sounds of the sea
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BOOKS & ARTS
Photography: Mark Fischer, Science Photo Library
WHALES and dolphins are accomplished vocalists, emitting complex patterns of clicks and whistles that vary in pitch, volume and length. To visualise their songs, and therefore identify species, marine biologists usually produce a spectrogram, a graph of how the frequency of their vocalisations varies over time. Spectrograms are created using a mathematical process called the Fourier transform (FT), which can convert raw sound into a set of sinusoidal waves. However,
46 | NewScientist | 30 January 2010
because these waves are periodic and infinite, they are better suited to describing repetitive, continuous noises, such as the whirr of a propeller, rather than the staccato clicks and whistles of cetaceans. Now Mark Fischer, an expert in marine acoustics, has come up with another way to illustrate whale song. He uses a more obscure method, known as the wavelet transform, which represents the sound in terms of components known as wavelets: short, discrete waves that are better at capturing cetacean song. The
picture above represents the lowfrequency moans and cries of a humpback whale’s mating song, plotted using a wavelet transform. The time axis is read anticlockwise. On a spectrogram it can be difficult to distinguish between similarsounding species, particularly if the animal clicks very rapidly, because these get smeared out in an FT. With the wavelet method, the clicks show up as precise spikes. As well as illustrating more characteristics of the sound, Fischer has taken advantage of the striking
look of his graphs, selling them as art through his company Aguasonic Acoustics, based in San Francisco. He has also been approached by the US navy, which is interested in using his technique to identify whales off the coast of the Bahamas and southern California. Some species are panicked by the sonar waves that naval vessels emit, so the navy needs an easy way to identify which creatures are nearby. Jessica Griggs ■ See whale-song art at bit.ly/8a85D3
AGUASONIC ACOUSTICS/SPL
Transforming the sounds of the sea
BOOKS & ARTS
Photography: Mark Fischer, Science Photo Library
WHALES and dolphins are accomplished vocalists, emitting complex patterns of clicks and whistles that vary in pitch, volume and length. To visualise their songs, and therefore identify species, marine biologists usually produce a spectrogram, a graph of how the frequency of their vocalisations varies over time. Spectrograms are created using a mathematical process called the Fourier transform (FT), which can convert raw sound into a set of sinusoidal waves. However,
46 | NewScientist | 30 January 2010
because these waves are periodic and infinite, they are better suited to describing repetitive, continuous noises, such as the whirr of a propeller, rather than the staccato clicks and whistles of cetaceans. Now Mark Fischer, an expert in marine acoustics, has come up with another way to illustrate whale song. He uses a more obscure method, known as the wavelet transform, which represents the sound in terms of components known as wavelets: short, discrete waves that are better at capturing cetacean song. The
picture above represents the lowfrequency moans and cries of a humpback whale’s mating song, plotted using a wavelet transform. The time axis is read anticlockwise. On a spectrogram it can be difficult to distinguish between similarsounding species, particularly if the animal clicks very rapidly, because these get smeared out in an FT. With the wavelet method, the clicks show up as precise spikes. As well as illustrating more characteristics of the sound, Fischer has taken advantage of the striking
look of his graphs, selling them as art through his company Aguasonic Acoustics, based in San Francisco. He has also been approached by the US navy, which is interested in using his technique to identify whales off the coast of the Bahamas and southern California. Some species are panicked by the sonar waves that naval vessels emit, so the navy needs an easy way to identify which creatures are nearby. Jessica Griggs ■ See whale-song art at bit.ly/8a85D3
AGUASONIC ACOUSTICS/SPL
Transforming the sounds of the sea