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Hearing, or audition, depends on the presence of sound waves, which travel much more slowly than light waves. Sound waves are changes in pressure generated by vibrating molecules. The physical characteristics of sound waves influence the three psychological features of sound: loudness, pitch, and timbre.

  • Loudness depends on the amplitude, or height, of sound waves. The greater the amplitude, the louder the sound perceived. Amplitude is measured in decibels. The absolute threshold of human hearing is defined as 0 decibels. Loudness doubles with every 10-decibel increase in amplitude.
  • Pitch, though influenced by amplitude, depends most on the frequency of sound waves. Frequency is the number of times per second a sound wave cycles from the highest to the lowest point. The higher the frequency, the higher the pitch. Frequency is measured in hertz, or cycles per second. Frequency also affects loudness, with higher-pitched sounds being perceived as louder. Amplitude and frequency of sound waves interact to produce the experiences of loudness and pitch.
  • Timbre, or the particular quality of a sound, depends on the complexity of a sound wave. A pure tone has sound waves of only one frequency. Most sound waves are a mixture of different frequencies.

The Structure of the Ear

Knowing the basic structure of the ear is essential to understanding how hearing works. The ear has three basic parts: the outer ear, the middle ear, and the inner ear.