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PSYB51H3 (306)
Chapter 9

PSYB51 Chapter 9

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Matthias Niemeier

Chapter 9: Hearing: Physiology and Psychoacoustics The Function of Hearing What Is Sound? - Sounds are created when objects vibrate causing molecules and objects surrounding medium to vibrate which causes pressure changes in the medium these pressure changes are described as waves - Sound waves do not change as they spread out, the initial amount of wave pressure is dispersed over a larger and larger area as the wave moves away, so the wave becomes less prominent as it gets farther from its source Sound waves travel faster through denser substances in error 340 ms, and water 1500 ms Basic Qualities of Sound Waves: Frequency and Amplitude - Soundwaves that we here are fluctuations in air pressure across time - Amplitude magnitude of displacement of a sound pressure waves or of a head movement - Intensity the amount of sound energy ball in on a unit area - We typically described sound wave patterns by noting how quickly the pressure fluctuates; the rate of fluctuation is known as the frequency Hertz a unit of measurement for frequency. 1 Hz equals one cycle per second - Amplitude is associated with the perceptual quality of loudness (psychological aspect of sound related to perceived intensity or magnitude) - Frequency is associated with pitch (psychological aspect of sound related mainly to the fundamental frequency) - Relatively young people are able to detect sounds that vary from about 20 to 20,000Hz - To describe differences in amplitude across such a broad range, sound levels are measured on a logarithmic scale using units called decibels (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, so a 100:1 ratio is equal to 40 dB Equation (page 221): dB = 20 log (p p ) If the pressure of the sound that youre measuring is equal to 0.0002 dyne cm, then dB = 20 log(1) because the log of one and zero, a sound pressure that low would be equal to 0 dB - Relatively small decibel changes can correspond to large physical changes for example an increase of 6 dB doubles the amount of pressure 1 www.notesolution.comSine Waves, Complex Tones, Fourier Analysis - Sinewave pure tone the waveform for which variation as a function of time is a sine function The air pressure in a sine wave changes continuously at the same frequency - Period the time or space required for one cycle of a repeating waveform - Phase the relative position of two or more sine waves. For sounds, the phase of the relative position and time - The undulation of the sine wave overtime is described in degrees - Sine waves are not common because few vibrations in the world are so pure - Complex tones a sound wave consisting of more than one sinosoidial component of different frequencies - All sounds can be described as a combination of sine waves Fourier analysis - In mathematical theorem by which any sound can be divided into a set sideways. Combining these sine waves will produce the original sound - Spectrum a representation of the relatives energyintensity present at each frequency - Sounds with harmonic spectra the spectrum of a complex sound in which energy is at integer multiples of the fundamental frequency are typically caused by a simple vibrating source - Each frequency component in such a sound is called a harmonic the first harmonic, called the fundamental frequency - The properties of sound sources determine the spectral shapes of sounds; these shapes can help us identify sound sources - Timbre psychological sensation by which a listener can judge that to sound the same loudness and pitch are dissimilar. Its quality is conveyed by harmonics and other high frequencies Basic Structure of the Mammalian Auditory System Outer Ear - Sounds are first collected from the environment by the Pinna which we usually call the ear Only mammals have these - Sound waves are funneled by the pinna into and through the ear canal which enhances sound frequencies between about 2000 and 6000Hz and whose main purpose is to insulate the structure at its end, the Tympanic membrane (a sheet of skin that moves in and out in response to the pressure changes of sound waves) Middle Ear - The pinna and the ear canal makeup the outer ear (the external gathering portion of the ear) 2 www.notesolution.com
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