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class+12+lecture_posted - Sensation and Perception Class...

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Sensation and Perception Class XII: Hearing Physiology
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Hearing: Physiology and Psychoacoustics 9
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What Is Sound? Sounds are created when objects vibrate Vibrations of an object cause molecules in the object’s surrounding medium to vibrate as well, which causes pressure changes in the medium
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Figure 9.1 The pattern of pressure fluctuations of a sound stays the same as the sound wave moves away from the source, but the amount of pressure change decreases with distance
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What Is Sound? Sound waves travel at a particular speed Depends on the medium Example: Speed of sound through air is about 340 meters/second, but speed of sound through water is 1500 meters/second
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What Is Sound? Physical qualities of sound waves: Amplitude : The magnitude of displacement of a sound pressure wave Intensity : The amount of sound energy falling on a unit area Frequency : For sound, the number of times per second that a pattern of pressure repeats
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What Is Sound? Units for measuring sound: Hertz (Hz): A unit of measure for frequency. One Hz equals one cycle per second Decibel (dB): A unit of measure for the physical intensity of sound Decibels define the difference between two sounds as the ratio between two sound pressures Each 10:1 sound pressure ratio equals 20 dB, and a 100:1 ratio equals 40 dB
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What Is Sound? Psychological qualities of sound waves: Loudness : The psychological aspect of sound related to perceived intensity or magnitude Pitch : The psychological aspect of sound related mainly to the fundamental frequency
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What Is Sound? Frequency is associated with pitch Low-frequency sounds correspond to low pitches Example: Low notes played by a tuba High-frequency sounds correspond to high pitches
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Figure 9.2 Sound waves are described by the frequency and amplitude of pressure fluctuations
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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
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This note was uploaded on 11/17/2011 for the course PSYCHOLOGY 830:301 taught by Professor Staff during the Spring '10 term at Rutgers.

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class+12+lecture_posted - Sensation and Perception Class...

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