Sound investment: A new mathematical method provides a better way to ana...( -tuned FM radio -- because it's the mos...)

-tuned FM radio -- because it's the most complex sound available, with exactly the same amount of energy at all frequency levels. When they plugged their algorithm into a computer, it reassigned each tone and plotted the data points on a graph in which the x-axis was time and the y-axis was frequency. The resulting histograms showed thin, froth-like images, each "bubble" encircling a blue spot. Each blue spot indicated a zero, or a moment during which there was no sound at a particular frequency. "There is a theorem," Magnasco says, "that tells us that we can know what the sound was by knowing when there was no sound." In other words, their pictures were being determined not by where there was volume, but where there was silence.

"If you want to show that your analysis is a valid signal estimation method, you have to understand what a sound looks like when it's embedded in noise," Magnasco says. So he added a constant tone beneath the white noise. That tone appeared in their histograms as a thin yellow band, bubble edges converging in a horizontal line that cut straight through the center of the froth. This, he says, proves that their algorithm is a viable method of analysis, and one that may be related to how the mammalian brain parses sound.

"The applications are immense, and can be used in most fields of science and technology," Magnasco says. And those applications aren't limited to sound, either. It can be used for any kind of data in which a series of time points are juxtaposed with discrete frequencies that are important to pick up. Radar and sonar both depend on this kind of time-frequency analysis, as does speech-recognition software. Medical tests such as electroencephalograms (EEGs), which measure multiple, discrete brainwaves use it, too. Geologists use time-frequency data to determine the composition of the ground under a surveyor's feet, and an angler's fishfinder uses the method to determine the water's depth and locate schools o
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Contact: Kristine Kelly
kkelly@rockefeller.edu
212-327-7146
Rockefeller University
26-Jul-2006

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