Hearing Detection Loudness Localization Scene Analysis Music
Speech
Slide 2
Detection and Loudness Sound level is measured in decibels (dB)
- a measure of the amplitude of air pressure fluctuations
Slide 3
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
Slide 4
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!
Slide 5
Detection and Loudness minimum sound level necessary to be
heard is the detection threshold
Slide 6
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
Slide 7
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)
Slide 8
Detection and Loudness Loudness is the subjective impression of
sound level (and not identical to it!)
Slide 9
Detection and Loudness For example, tones of different
frequencies that are judged to be equally loud have different SPLs
(dB)
Slide 10
Detection and Loudness Hearing loss due to exposure to
high-intensity sounds (greater than 100 dB) is frequency-specific
and can last many hours
Slide 11
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 its hard to tell how
loud your iPod is - LOCK THE VOLUME ON YOUR iPOD!
Slide 12
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 Auditory Scene Analysis
Slide 13
All you have is a pair of instruments (basilar membranes) that
measure air pressure fluctuations over time Localization
Slide 14
There are several clues you could use: Localization
Slide 15
Left Ear Right Ear Compression Waves
Slide 16
There are several clues you could use: 1 arrival time - sound
arrives first at ear closest to source Localization
Slide 17
Left Ear Right Ear Compression Waves
Slide 18
There are several clues you could use: 1.arrival time 2.phase
lag (waves are out of sync) - wave at ear farthest from sound
source lags wave at ear nearest to source Localization
Slide 19
Left Ear Right Ear Compression Waves
Slide 20
There are several clues you could use: 1.arrival time 2.phase
lag (waves are out of sync) - wave at ear farthest from sound
source lags wave at ear nearest to source 3.Head shadow
Localization
Slide 21
Arrival Time Phase Lag Head Shadow Interaural Timing
Differences (ITD) Interaural Intensity Difference (IID)
Slide 22
What are some problems or limitations? Localization
Slide 23
Low frequency sounds arent attenuated by head shadow
Localization Left Ear Right Ear Compression Waves Sound is the same
SPL at both ears
Slide 24
Low frequency sounds arent attenuated by head shadow Your brain
preferentially uses ITD cues for low-frequency sounds
Localization
Slide 25
High frequency sounds have ambiguous phase lag Localization
Left Ear Right Ear Left Ear Right Ear Two locations, same phase
information!
Slide 26
High frequency sounds have ambiguous phase lag Your brain
preferentially uses IID cues for high-frequency sounds
Localization
Slide 27
These cues only provide azimuth (left/right) angle, not
altitude (up/down) and not distance Localization Left Ear Right Ear
Azimuth
Slide 28
Localization Additional cues:
Slide 29
Localization Additional cues: Head Related Transfer Function:
Pinnae modify the frequency components differently depending on
sound location
Slide 30
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
Slide 31
Localization What would be the worst case scenario for
localizing a sound?