How can a medium carry multiple sounds at once?

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Discussion Overview

The discussion revolves around how a medium, specifically air composed of diatomic gases, can carry multiple sound waves simultaneously. Participants explore the mechanisms of sound propagation, the role of individual molecules, and the auditory processing of complex sound waves.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether individual molecules can vibrate and propagate multiple sound waves simultaneously or if different groups of molecules carry different sounds.
  • Another participant suggests that the pressure waves combine to form a single overall wave, which is then separated into distinct sounds by the brain through a process akin to Fourier analysis.
  • A follow-up inquiry is made regarding the maximum complexity or amplitude of sound that air can carry, implying there may be limits to human auditory perception.
  • Some participants note that different species have varying auditory ranges due to evolutionary adaptations, suggesting that hearing everything may not be advantageous.
  • A clarification is provided that frequency separation occurs in the ear rather than the brain, with a reference to the basilar membrane's role in this process.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms of sound separation and the roles of the ear and brain, indicating that multiple competing views remain without a consensus on the specifics of sound propagation and auditory processing.

Contextual Notes

There are unresolved questions regarding the limits of sound complexity in air and the specific roles of different molecules in sound propagation, as well as the implications of auditory processing across species.

Richa
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When one hears a police siren, music, and a car alarm all at once, how can these multiple types of vibrations be accommodated by the medium? (Let's take the simple case of the diatomic gases in air.) Is it possible for individual molecules to vibrate and propagate multiple sound waves at once, or do different groups of molecules somehow end up carrying a certain sound, while other groups carry the other sound? Do they "trade roles" quickly? Is oxygen more apt to carry certain types of sounds than nitrogen? In the case of one sound, do all/most molecules vibrate to propagate the sound, or only a small amount?

Thank you for your wisdom!
 
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The pressure waves add to give one overall pressure wave, and that's all that our eardrum and inner ear detects. What separates it out into separate sounds is our remarkable brains, which I suspect perform a type of Fourier analysis on the waveform to split the single wave into separate waves of different frequencies. It's a pretty stunning feat when you think about it, but then brains are pretty amazing things.
 
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It is very stunning indeed. Fourier analysis of any kind seems like a miracle. A follow-up question then: Is there a maximum complexity or amplitude of sound that can be carried by normal air? (I assume there is a limit to what our ears can detect, correct?)
 
Sure, there is a limit to sounds that human ears can detect. other species have their own range as a result of what worked for natural selection in their case.
Hearing 'everything' is of no advantage, it's just white noise.
 
andrewkirk said:
What separates it out into separate sounds is our remarkable brains, which I suspect perform a type of Fourier analysis on the waveform to split the single wave into separate waves of different frequencies.
The frequency splitting is done by the ear, not by the brain:
https://en.wikipedia.org/wiki/Basilar_membrane#Frequency_dispersion
 
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A.T. said:
The frequency splitting is done by the ear, not by the brain
Thanks. Great link. What an amazing mechanism!
 

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