Transcript PowerPoint Presentation - MUSTH 125: Hearing (Chapter 5)

Hearing
Chapter 5
Range of Hearing
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Sound intensity (pressure) range runs
from 10-13 watts to 50 watts.
Frequency range is 20 Hz to 20,000 Hz,
or a ratio of 103 between highest and
lowest frequencies.
Intensity
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Power
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Pressure
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Rate of work (Work/Time)
Force per unit area (F/A)
Intensity
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Power per unit area carried by a wave,
expressed in watts/square meter (W/m2).
Frequency
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Unusual to find someone who can hear the
entire “normal” range of 20 — 20,000 Hz.
Structure of Ear
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3 Parts: Outer, Middle, Inner
Outer: Pinna and auditory canal,
terminated at ear drum.
Middle: begins with ear drum, ossicles
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Ossicles function as mechanical
transformer
Eustachian tube
Inner: semi-circular canals and cochlea.
Transduction
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Transduction is the process of
transforming energy from one form to
another.
Middle Ear: changes in air pressure to
mechanical energy
Inner Ear: mechanical pressure to
hydraulic variations to neural impulses
(electrical)
The Ear
The Outer Ear
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Pinna
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Helps to collect sound and aids in the
localization of high sounds (above 4 kHz).
Auditory Canal
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Acts as a pipe resonator that boosts
hearing sensitivity in the range of 2 kHz to
5 kHz.
Middle Ear
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Eardrum
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Variations in air pressure are changed to
mechanical vibrations.
Ossicles
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Act as a lever, changing small pressure
exerted on eardrum into a much greater
pressure on the oval window.
Inner Ear
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Semi-circular canals affect balance
Cochlea
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Receives pressure variations from stapes
onto Oval Window.
Transforms pressure variations into
mechanical vibrations of basilar
membrane,
and into properly coded neural impulses.
Cochlea
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Filled with two types of fluid
Basilar membrane
Organ of Corti
Hair Cells
Frequency detection, but not pitch.
Basilar Membrane
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Amplitude of displacement varies by
distance (from stapes) as a function of
frequency.
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Higher frequencies show displacement
closer to stapes than lower frequencies.
Signal Processing and Critical
Bands
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Critical Bands relate to overlap on the
basilar membrane.
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From Rossing, when two pure tones are so
close in frequency that there is
considerable overlap in the amplitude
envelopes on the basilar membrane, they
are said to lie within the same critical band.
Critical Bands
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Approx. 24
Critical Bandwidth varies with center
frequency.
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1/3-octave for most of the hearing range
Sound Localization
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Binaural hearing (Two ears), aids in localizing
sound.
Below 1000 Hz, localization is due to interaural time differences and phase differences.
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Precedence effect (Haas effect)
Above 4000 Hz, localization is due to intensity
differences.
Between 1 kHz and 4 kHz, our ability to
localize sound takes a nose-dive.
Psychophysics
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The relation of sensation to perception.
Multiplication of sensation leads to
addition of perception.
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logarithmic
Logarithms
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A logarithm is a relationship between a
base and that base raised to a power.
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100 = 102 so log10100 = 2 (log100 = 2)
Helps in expressing a ratio relationship
between sensation and perception.
Related to exponents and scientific
notation (discussed earlier)
Logarithmic Identities
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log AB = log A + log B
log A/B = log A - log B
log An = n log A