![]() “This information at the third frequency is something that we haven’t traditionally had before,” he said. He mathematically combines any two frequencies within the signal’s recorded frequency range, to reveal information outside that range at a new, third frequency that is the sum or difference of the two input frequencies. With the recorded sound translated into frequencies, Dowling puts his technique to use. Through a mathematical calculation known as a Fourier transform, sound amplitude versus time can be converted to sound amplitude versus frequency. Both images were created from the same sound recordings.Īny time sound is recorded, a microphone takes the role of the human ear, sensing sound amplitude as it in varies in time. ![]() This is what a listening system ‘sees’ with traditional signal processing (left) and with the new techniques (right). Sounds with frequencies higher than an array’s intended range may confuse the system it might be able to detect the presence of an important contact, but still be unable to locate it. Sonar arrays are typically designed to record sounds in specific frequency ranges. The ability to detect and locate enemy ships at sea is a crucial task for naval vessels. Navy sonar arrays on submarines and surface ships deal with a similar kind of confusion as they search for vessels on the ocean surface and below the waves. The techniques my students and I have developed will allow just about any signal to be shifted to a frequency range where you’re no longer confused. “The techniques my students and I have developed will allow just about any signal to be shifted to a frequency range where you’re no longer confused,” said Dowling, whose research is primarily funded by the U.S. The higher frequency of the smoke alarm sound creates directional confusion for the human ear. That annoying screech is generated by sound waves at higher frequencies, and in the midst of them, it would be difficult for you to locate the source of the screech without opening your eyes for additional sensory information. Now, imagine yourself in the same room when a smoke alarm goes off. Speech frequencies are right in the comfort zone for human hearing. Sitting in a room with your eyes closed, you would have little trouble locating someone speaking to you at normal volume without looking. He likens his approach to solving the problem of human sensory overload. “Acoustic fields are unexpectedly richer in information than is typically thought,” said David Dowling, a professor in U-M’s Department of Mechanical Engineering. That additional information could boost performance of passive sonar and echolocation systems for detecting and tracking adversaries in the ocean, medical imaging devices, seismic surveying systems for locating oil and mineral deposits, and possibly radar systems as well. By essentially turning down the pitch of soundwaves, University of Michigan engineering researchers have devised a way to unlock greater amounts of data from acoustic fields than ever before.
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