How the Ear Works
Watch this video about how the ear detects sound waves, and then sorts out the frequencies that make up the sound waves.
In class, I plan to demonstrate sound waveforms and to sort them into component frequencies. See Technical Notes, bottom of page.
Here is an image of the sound wave that reaches your ear when I whistle at about 1450 Hz (around F#6 on the piano, where C4 is middle C). Your ear drum would vibrate as shown here.
A. Whistle Wave Form
Here is the kind of thing that your cochlea does with that sound wave. It distills or sorts the single into its component frequencies, and sends each narrow range of frequencies to the brain as separate signals by separate nerve paths.
B. Whistle Frequency Analysis (for you mathematicians, the fourier transform of A.)
Notice that the strongest frequency is that of my whistle, but there are other frequencies in the ambient sound of my environment, as well as in my whistle itself, which include its overtones and the inevitable hissing I make in forcing air through my lips (fine peaks at higher frequencies). These frequencies are apparent in wave form A only as trace irregularities in the wave form, but they are easily visible in B, showing that they can be teased out into the open by frequency analysis, or by a cochlea.
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Technical Notes
All signal images and displays in class collected on iPhone using the DecibelX Pro app with the iPhone built-in microphone. App available at Apple App Store (~$5.00). Fun and interesting way to analyze sounds around you, and can alert you if your environment is noisy enough to damage your hearing.
You can make video recordings of images by connecting your phone to your computer, running Quicktime Player, selecting New Movie, and choosing the iPhone as your camera, using the tiny, barely noticeable menu on the recording panel. (By the way, this is a good way to project an image of your phone onto your computer.)
