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Chapter 9

PSYB51H3 Chapter 9: Hearing: Physiology & Psychoacoustics

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Matthias Niemeier

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PSYB51: Sensation & Perception
Chapter 9: Hearing: Physiology & Psychoacoustics
March 19, 2017
Wei Luo
The Function of Hearing
The next three chapters will cover three main topics: the nature of sound, the anatomy and physiology of the auditory
system, and how we perceive the two fundamental sound qualities which are loudness and pitch
What is Sound?
Sound are created when the vibration of the object occurs; the sound source comes from the vibration of the objection
which will cause the molecules in the object’s surrounding such as the earth’s atmosphere to also vibrate as well
o The vibration will cause pressure to change in the medium (the object’s surrounding)
These pressures changes can be called as waves; these waves are similar to the waves
on a pond which are only caused when dropping a rock into the water
o With the rock being thrown into the water, the water molecules that is caused by the
rock will not travel far enough
This is because, the wave has its limits due to other sources outside of the rock will
get in the way to allow the molecules to travel far
E.g. the shore, a boat, a swimming duck or anything else
o The pattern of the pond as well as the waves will not change as they spread across
(stays constant), however, the amount of pressure change will spread across the pond as the
waves move away (Figure 9.1)
Therefore, the wave will become less as important as it moves farther away from its
The speed of the sound wave will depend on the object
o E.g. the speed of air will travel at about 340m per second which depends on the whether such as sounds travel
faster on muggy day
However, sound travelling through water is a lot slower; it travels at about 1500m per second
o Light waves move ten times faster than sound waves, which is why in days with thunderstorms, we will see the
lightening first before hearing the thunder at least about 1 second per mile
Basic Qualities of Sound Waves: Frequency and Amplitude
The sound waves we
here in our environment varies
due to air pressure across time
o The intensity or the
magnitude of the pressure change
in a sound wave (the difference
between the highest pressure and
the lowest pressure) is simply
called Amplitude or Intensity of
the wave
o The changes of pressure
can either be very close together
or spread apart for a longer period of time
Sound waves and light waves both have wavelengths, however, to describe the wavelengths for sound waves, you
describe them by how fast the pressure changes which is known to be as Frequency of the wave

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AMPLITUDE OR INTENSITY The magnitude of displacement (increase or decrease) of a sound pressure wave. Amplitude
can be perceived as loudness
FREQUENCY For sound, the number of times per second that a pattern of pressure change repeats. Frequency is perceived
as pitch
Sound wave frequencies’ unit of measure is called a Hertz (Hz), which is when 1 cycle per second equals 1 Hz
HERTZ (Hz) A unit of measure for frequency. One hertz equals one cycle per second
Amplitude and frequency is closely related to auditory characteristics
o As mentioned before, amplitude is associated with Loudness and frequency is associated with Pitch
o Loudness can be known as the more intense a sound wave is, the louder it will sound
o Pitch for example, low-frequency sounds is corresponded to low pitch (e.g. playing low notes played by a
With high frequency sounds is corresponded to high pitch (e.g. playing high notes by a flute)
A regular human being is able to detect sound between about 20 to 20,000 Hz
Animals and humans are different when coming to hearing sounds; some can hear sounds with low frequencies or high
frequencies or even both at the same time
o Larger animals are better at hearing low frequencies and smaller animals generally are better at hearing high
o Elephants hear vibrations when at low frequencies in order to help them detect their own species or other
larger animals
The intensity of sounds that humans can detect are between the faintest sounds and the loudest sounds that do not cause
any damage to their hearing
To describe the amplitude, sounds
can be measured through an equation on a
logarithmic scale using units called
decibels (dB) and the equation to describe
the measurement is dB = 20 log(p/p0) (the
zero is put at the bottom of the p)
o With this measurement, small
decibel changes relate to physical changes
E.g. if you increase 6dB can
double the amount of pressure (Figure 9.4
sounds that we hear in our daily
environments vary greatly in intensity)
DECIBLES (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
Sine Waves and Complex Sounds
The simplest sound we know is called Sine Waves or also known as Pure Tone
o The combination of sounds can describe complex sounds such as musical instruments, human speech and city
SINE WAVE OR PURE TONE Th waveform for which variation as a function of time is a sine function
Complex sounds are best to be described as Spectrum when it has too much things going on or too much amplitude and
that it presents multiple frequencies (Figure 9.5)

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Many common sounds have
Harmonic Spectre (Figure 9.6)
Simple vibration causes harmonic
Spectre such as from the strings of a guitar
For component of the frequency
is known as the Harmonic and that the very
first harmonic is called Fundamental
Frequency which is the lowest frequency
component of the sound
Other harmonics have frequencies
that are integer multiples of the
of a complex sound in which energy is at
integer multiples of the fundamental frequency
FUNDAMENTAL FREQUENCY The lowest-frequency component of a
complex sound
(Figure 9.6 shows that Harmonic sounds the same fundamental frequency can
sound different because amplitudes of individual frequency components are
different, resulting in different spectral shapes. For example, different musical
instruments playing the same note)
One of the most important ways to tell the difference of sounds is through
the shape of the spectrum or spectral shape
o To determine the shapes of the spectrum is through the sources of
the sounds coming out from the medium; the shapes of these
spectrum can vary as well
This can be determined through Figure 9.6
Another way to determine the difference of sounds is through Timbre that is
to describe the quality of the sound that depends on the energy levels of
harmonic components
TIMBRE The psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are
not the same. Harmonics and other high frequencies express timbre quality
Basic Structures of the Mammalian Auditory System
Outer Ear
When sounds are produced, the first thing that we pick up sound is through our Pinna or our Ear
o Only mammals have pinnae, and they come in different shapes and sizes across them but varies less in human
o The most important thing about pinna, is that the shape of it plays an important role in order for us to collect
PINNA The outer, funnel-like part of the ear
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