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) is frequency-specific
and 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!
Auditory Scene Analysis
• 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
– Identify the sources of those ripples
– Ignore non-relevant ripples
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
•
1
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
•
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
•
1.
2.
3.
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
Head shadow
Localization
• Arrival Time
• Phase Lag
Interaural Timing Differences (ITD)
• Head Shadow
Interaural Intensity Difference (IID)
Localization
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What are some problems or
limitations?
Localization
•
Low frequency sounds aren’t
attenuated by head shadow
Sound is the same
SPL at both ears
Left Ear
Right Ear
Compression
Waves
Localization
•
Low frequency sounds aren’t
attenuated by head shadow
•
Your brain preferentially uses ITD
cues for low-frequency sounds
Localization
•
Left Ear
High frequency sounds have
ambiguous phase lag
Left Ear
Right Ear
Right Ear
Two locations, same phase information!
Localization
•
High frequency sounds have
ambiguous phase lag
•
Your brain preferentially uses IID
cues for high-frequency sounds
Localization
•
These cues only provide azimuth
(left/right) angle, not altitude
(up/down) and not distance
Left Ear
Right Ear
Azimuth
Localization
Additional cues:
Localization
Additional cues:
Head Related Transfer Function:
Pinnae modify the frequency
components differently depending on
sound location
Localization
Additional cues:
Room Echoes:
For each sound, there are 6
“copies” (in a simple
rectanguluar room!).
Different arrival times of
these copies provide cues
to location of sound
relative to the acoustic
space
Localization
• What would be the “worst case”
scenario for localizing a sound?