What do we hear?
• Sound is a compression wave - it only “looks”
like a wave if we plot air pressure against time
Period - amount of time for one cycle
Frequency = number
of cycles per second
(1/Period)
Air Pressure
time ->
Sensing Vibrations
• Inside the cochlea is the basilar membrane
• Movement of the oval window causes ripples
on the basilar membrane
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!