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
• 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)
• 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:
1
arrival time - sound arrives first at ear
closest to source
Localization
Left Ear
Right Ear
Compression
Waves
Localization
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1.
2.
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
Localization
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1.
2.
3.
There are several clues you could use:
arrival time
phase lag (waves are out of sync)
sound shadow (intensity difference)- sound
is louder at ear closer to sound source
Localization
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What are some problems or limitations?
Localization
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Low frequency sounds aren’t attenuated
by head shadow
Sound is the same
SPL at both ears
Left Ear
Right Ear
Compression
Waves
Localization
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Left Ear
Right Ear
High frequency sounds have ambiguous
phase lag
Left Ear
Right Ear
Two locations, same phase information!