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No, it's different. That's a real beating effect. This is an phenomenon that happens when the two tones are heard separately in each ear and the beating just

No, it's different. That's a real beating effect. This is an phenomenon that happens when the two tones are heard separately in each ear and the beating just happens in your head. It tells us that our auditory system retains some waveform data, up to about 1000 Hz.

bigiain 13y ago
This is what I find fascinating about it. I understand from a math/physics perspective why a microphone places betwen two sound sources playing slightly different frequencies "hears" the beat pattern. I don't understand why that still works once the two individual signals have made their way into your audio nerves and brain. (If I didn't have actual work I shoukd be doing now, I suspect I'd happily drop into a 6 or 8 hour wikipedia and google mediated deep-dive laymans research session.)
- iyulaev 13y ago
  It's a phenomenon that happens to all waves, whether they are acoustic or electromagnetic. In fact, it's how your clock radio tunes to various stations. This property is a mathematical property of all waves, hence even when your brain mixes an electrical representation of the sound going into your left and right ears, you still get the effect.
  - mdturnerphys 13y ago
    For higher frequencies your auditory system doesn't retain the waveform information, so this doesn't happen.
    - bigiain 13y ago
      I wonder if that's an evolutionary thing – somehow we evolved out the ability to retain phase difference information outside the frequencies where it's useful for stereo angular location? The "~1000Hz" upper limit is pretty close to a 1/4 wavelength for a "phased array" of two ears ~100mm apart. That'd make it pretty ideal for angular discrimination based on phase difference.
      - apl 13y ago
        You're pretty spot on here -- up to approximately 1500Hz, the auditory brain can make use of so-called inter-aural time differences which allow estimation of a given source's azimuth. After that, phase differences become ambiguous and the brain relies more heavily on inter-aural volume differences. http://en.wikipedia.org/wiki/Interaural_time_difference http://en.wikipedia.org/wiki/Interaural_time_difference

bigiain 13y ago

This is what I find fascinating about it. I understand from a math/physics perspective why a microphone places betwen two sound sources playing slightly different frequencies "hears" the beat pattern. I don't understand why that still works once the two individual signals have made their way into your audio nerves and brain. (If I didn't have actual work I shoukd be doing now, I suspect I'd happily drop into a 6 or 8 hour wikipedia and google mediated deep-dive laymans research session.)

iyulaev 13y ago
It's a phenomenon that happens to all waves, whether they are acoustic or electromagnetic. In fact, it's how your clock radio tunes to various stations. This property is a mathematical property of all waves, hence even when your brain mixes an electrical representation of the sound going into your left and right ears, you still get the effect.
- mdturnerphys 13y ago
  For higher frequencies your auditory system doesn't retain the waveform information, so this doesn't happen.
  - bigiain 13y ago
    I wonder if that's an evolutionary thing – somehow we evolved out the ability to retain phase difference information outside the frequencies where it's useful for stereo angular location? The "~1000Hz" upper limit is pretty close to a 1/4 wavelength for a "phased array" of two ears ~100mm apart. That'd make it pretty ideal for angular discrimination based on phase difference.
    - apl 13y ago
      You're pretty spot on here -- up to approximately 1500Hz, the auditory brain can make use of so-called inter-aural time differences which allow estimation of a given source's azimuth. After that, phase differences become ambiguous and the brain relies more heavily on inter-aural volume differences. http://en.wikipedia.org/wiki/Interaural_time_difference http://en.wikipedia.org/wiki/Interaural_time_difference