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Hearing
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Detection
Loudness
Localization
Scene Analysis
Music
Speech
Detection and Loudness
• Sound level is measured in decibels
(dB) - a measure of the amplitude of
air pressure fluctuations
Detection and Loudness
• Sound level is measured in decibels
(dB) - a measure of the amplitude of
air pressure fluctuations
• dB is a log scale - small increases in
dB mean large increases in sound
energy
Detection and Loudness
• Sound level is measured in decibels
(dB) - a measure of the amplitude of
air pressure fluctuations
• dB is a log scale - small increases in
dB mean large increases in sound
energy
• We have a dynamic range that is a
factor of 7.5 million!
Detection and Loudness
• minimum sound level necessary to be
heard is the detection threshold
Detection and Loudness
• detection threshold depends on
frequency of sound:
• very high and very low frequencies
must have more energy (higher dB) to
be heard
• greatest sensitivity (lowest detection
threshold) is between 1000 hz to
5000hz
Detection and Loudness
• Detection can be compromised by a
masking sound
• even masking sounds that are not
simultaneous with the target can
cause masking (forward and
backward masking)
Detection and Loudness
• Loudness is the subjective impression
of sound level (and not identical to it!)
Detection and Loudness
• For example,
tones of
different
frequencies
that are judged
to be equally
loud have
different SPLs
(dB)
Detection and Loudness
• Hearing loss due to exposure to high-intensity
sounds (greater than 100 dB) can last many hours
Detection and Loudness
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Incidence of noise-related hearing loss is increasing dramatically
iPods and other “earbud” music players are thought to be partly responsible
How loud is an iPod?
– maximum volume is approximate but is somewhere between 100 dB (hearing
damage in about 2 hours) to 115 dB (hearing damage in about 15 minutes)
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Consequences: difficulty understanding speech, tinnitus, deafness
Your perception of loudness adapts so it’s hard to tell how loud your iPod is LOCK THE VOLUME ON YOUR iPOD!
Localization
• recall the lake analogy: task is to
localize the positions of the boats on a
lake using the pattern of ripples at two
points on the shore
Localization
• All you have is a pair of instruments
(basilar membranes) that measure air
pressure fluctuations over time
Localization
• There are several clues you could use:
Localization
Left Ear
Right Ear
Compression
Waves
Localization
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There are several clues you could
use:
arrival time - sound arrives first at ear
closest to source
Localization
Left Ear
Right Ear
Compression
Waves
Localization
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There are several clues you could
use:
arrival time
phase lag (waves are out of sync) wave at ear farthest from sound
source lags wave at ear nearest to
source
Localization
Left Ear
Right Ear
Compression
Waves