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class+13+lecture_posted (1) - Sensation and Perception...

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Sensation and Perception Class XIII: Hearing Physiology
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What Is Sound? Human hearing uses a limited range of frequencies (Hz) and sound pressure levels (dB)
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What Is Sound? Humans can hear across a wide range of sound intensities Ratio between faintest and loudest sounds is more than 1:1,000,000 In order to describe differences in amplitude, sound levels are measured on a logarithmic scale, in decibels (dB) Relatively small decibel changes can correspond to large physical changes § For example: An increase in 6 dB corresponds to a doubling of the amount of pressure
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Figure 9.4 Sounds that we hear in our daily environments vary greatly in intensity
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What Is Sound? One of the simplest kinds of sounds: Sine waves, or pure tone Sine wave : The waveform for which variation as a function of time is a sine function Period : The time required for one cycle of a repeating waveform Phase : The relative position of two or more sine waves § There are 360 degrees of phase across one period
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Figure 9.5 A sine wave is a circular motion extended over time
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What Is Sound? Sine waves are not common in everyday sounds because not many vibrations in the world are so pure Most sounds in the world are complex sounds § For example: Human voices, bird songs, car noises All sound waves can be described as some combination of sine waves
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Figure 9.6 Every complex sound wave can be analyzed as a combination of sine waves
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What Is Sound? Complex sounds can be described by Fourier analysis Fourier analysis : A mathematical theorem by which any sound can be divided into a set of sine waves § Combining these sine waves will reproduce the original sound
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Figure 9.7 A spectrum displays the amplitude for each frequency present in a sound wave
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What Is Sound? Harmonic spectrum : Typically caused by a simple vibrating source (e.g., string of a guitar, or reed of a saxophone) Fundamental frequency : The lowest-frequency component of a complex periodic sound Timbre : The psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are dissimilar § Timbre quality is conveyed by harmonics and other high frequencies
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Figure 9.8 Harmonic sounds with the same fundamental frequency can sound different
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Basic Structure of the Mammalian Auditory System How are sounds detected and recognized by the auditory system?
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Basic Structure of the Mammalian Auditory System Outer ear Sounds are first collected from the environment by the pinnae Sound waves are funneled by the pinnae into the
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class+13+lecture_posted (1) - Sensation and Perception...

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