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posted by martyb on Monday December 03 2018, @06:20AM   Printer-friendly
from the I-see^W-hear-what-ytou-did-there dept.

Revealing hidden information in sound waves

“Acoustic fields are unexpectedly richer in information than is typically thought,” said David Dowling, a professor in U-M’s Department of Mechanical Engineering.

[...] Sonar arrays are typically designed to record sounds in specific frequency ranges. 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.

Any time sound is recorded, a microphone takes the role of the human ear, sensing sound amplitude as it in varies in time. Through a mathematical calculation known as a Fourier transform, sound amplitude versus time can be converted to sound amplitude versus frequency.

With the recorded sound translated into frequencies, Dowling puts his technique to use. 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.

“This information at the third frequency is something that we haven’t traditionally had before,” he said.

In the case of a Navy vessel’s sonar array, that additional information could allow an adversary’s ship or underwater asset to be reliably located from farther away or with recording equipment that was not designed to receive the recorded signal. In particular, tracking the distance and depth of an adversary from hundreds of miles away—far beyond the horizon—might be possible.

And what’s good for the Navy may also be good for medical professionals investigating areas of the body that are hardest to reach, such as inside the skull. Similarly, remote seismic surveys that parse through the earth seeking oil or mineral deposits could also be improved.

[...] More information:


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  • (Score: 2) by Arik on Monday December 03 2018, @07:14AM (3 children)

    by Arik (4543) on Monday December 03 2018, @07:14AM (#769095) Journal
    Wait, you mean SONAR just discovered the overtone and undertone series?

    https://en.wikipedia.org/wiki/Undertone_series
    --
    If laughter is the best medicine, who are the best doctors?
  • (Score: 3, Informative) by Anonymous Coward on Monday December 03 2018, @08:11AM (2 children)

    by Anonymous Coward on Monday December 03 2018, @08:11AM (#769103)

    tracking the distance and depth of an adversary from hundreds of miles away—far beyond the horizon—might be possible.

    I can assure you that this has been the case since at least the 1970s, and I'd assume earlier, but I'm not that old.

    Also, I always love how people talking about sonar can't help but confuse active and passive sonar as seems to be done all over this summary.

    • (Score: 1) by anubi on Tuesday December 04 2018, @03:08AM

      by anubi (2828) on Tuesday December 04 2018, @03:08AM (#769416) Journal

      Its amazing how much info is in sound... Most of what I messed with was how harmonics and Doppler shifts interrelated, along with beamforming, using multiple microphones listening to the same source but from various spatial perspective.

      Just one tiny sound snippet was all it took to know what was making the noise, where it was, where it was going, and how fast. This was back in the 80's.

      --
      "Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
    • (Score: 2) by MichaelDavidCrawford on Tuesday December 04 2018, @11:18AM

      by MichaelDavidCrawford (2339) Subscriber Badge <mdcrawford@gmail.com> on Tuesday December 04 2018, @11:18AM (#769492) Homepage Journal

      They really _did_ listen, for the sound of oncoming air raids. Can I find a link?

      -~<{([LINK [google.com]])}>~-

      You won't need to click it if you can visualize Jesus Big Ear Trumpets.

      I hear quite poorly, however it helps quite a lot for me to wear wide-brimmed hats as they reflect sound into my ears.

      --
      Yes I Have No Bananas. [gofundme.com]
  • (Score: 0) by Anonymous Coward on Monday December 03 2018, @05:47PM

    by Anonymous Coward on Monday December 03 2018, @05:47PM (#769208)

    As long as the capture bandwidth of the microphones is sufficient, under sampling (sampling at below nyquist) can be used to detect signals outside of the nyquist frequency. This is used in radio frequency digital conversion, but is unnecessary at audio frequencies since ADCs are fast enough to capture the full bandwidth.

  • (Score: 2) by MichaelDavidCrawford on Tuesday December 04 2018, @11:12AM

    by MichaelDavidCrawford (2339) Subscriber Badge <mdcrawford@gmail.com> on Tuesday December 04 2018, @11:12AM (#769490) Homepage Journal

    Try blindfolding me sometime, then let me wander around a hallway with corners in it. I won't run into any of the walls.

    Really what I'm doing is not so much hearing but sensing the presence of the acoustic pressure of very low-frequency harmonics of the space I'm in. This takes some practice, but try it in a dark room with your eyes shut.

    As you slowly creep up closer and closer to a wall, you will feel it's presence several inches away. It's hard to describe the sensation as it's a very subtle thing, and these harmonic are way too low in frequency to hear, but their pressure is definitely higher the closer one is to a wall.

    This had me puzzled for years. I have what most people regard as uncommonly excellent night vision. That's not the case, rather that I can walk in pitch darkness without hesitation because I learned how avoid obstacles when doing so when I was twelve or so, and first got into amateur astronomy.

    --
    Yes I Have No Bananas. [gofundme.com]
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