Mechanics of Hearing & How the Brain Processes Sound

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  • 0:05 Sound Waves
  • 0:43 Frequency
  • 1:08 Loudness
  • 2:17 Processing Sound
  • 3:59 Pitch
  • 4:52 Lesson Summary
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Lesson Transcript
Instructor: Paul Bautista
How do our ears transform sound into signals that our brains can process? In this lesson, you'll cover properties of sound waves and how they interact with key parts of the ear.


Did you know where the smallest bones in your body are? They're not in your fingers and toes; they're actually in your ear, and they make up a part of the complicated mechanism that allows our ears to turn vibrations in the air into the sounds that we hear.

Sound Waves

Sound is made up of molecules vibrating in patterns called waves. When I bang on a drum, the drum's vibrating surface disturbs the air in patterns that, once they reach my ear, can be interpreted as a sound. Unlike light, which can travel in a vacuum through space, sound waves need material to travel--they need some sort of matter to disturb.


Sound waves that are shorter hit our ears in more rapid succession; they are said to have a higher frequency. Frequency is related to the idea of pitch in music, or the relative highness or lowness of a given sound. When an opera singer hits a high C, she is producing sound waves that are very short and with a high frequency. When a tuba plays a low C, its sound waves are much longer and with a lower frequency.


Loudness is related to another feature of the sound wave, called amplitude. Amplitude is basically the size, or height, of the sound wave. The bigger the wave, the louder the sound. You may have heard the term decibel ; that's a scale, rather like degrees for temperature, for saying how loud something is. Unlike degrees, however, the decibel scale is logarithmic. This means that if one sound is 10 decibels louder than another, it's actually ten times as loud. A 60 decibel conversation is ten times as loud as 50 decibel rainfall; a 110 decibel rock concert is ten times as loud as a 100 decibel snowmobile. A 90 decibel lawnmower is 100 times louder than a 70 decibel vacuum cleaner--ten times ten. The scale starts at the threshold of human hearing, so zero decibels represents the point at which a sound becomes so quiet that humans can't detect it. Prolonged exposure to noises above 85 decibels can cause hearing loss, either by physically damaging the ear or by damaging the nerves that transmit signals to the brain.

Interpreting Where Sound Is Coming From

You know how when you hear a noise, you can usually tell where it's coming from? This is because we have two ears, spaced apart on either sides of our heads. This means that if a sound is coming from the left, it reaches the left ear sooner than it reaches the right. While the difference in time might be really small, your brain automatically interprets this to help you determine where the sound is coming from.

Parts of the ear involved in hearing
Ear Parts

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