Blue whale (Balaenoptera musculus) song, wavelet graph. This image was produced by converting the sound frequencies of a blue whale song into a graph using a mathematical process known as wavelets. Wavelets reveal structure and detail that are not always visible in standard graphs of frequency over time (known as a spectrogram). This image has been plotted as a rectangular graph but wavelet graphs can also be in polar (circular) form. Blue whales produce songs containing variety of moans and pulses that are repeated over many hours. The songs, which can travel thousands of kilometres underwater, are at frequencies inaudible to humans and must be recorded using underwater hydrophones. Image created by Mark Fischer from Aguasonic Acoustics, USA.
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