Transcript Lecture03AP2008 - AbsoluteHearingThreshold

Applied Psychoacoustics
Lecture 2: Thresholds of Hearing
Jonas Braasch
Your best friend claims that his 100-Dollar
Boom-Box from a local retailer sound as good
as your High-end sound system.
Your sister claims that she hears events, while
you are confident that nothing can be heard.
Your band mate accuses you of changing the
pitch of your guitar with every time you tilt
your wah-wah pedal.
Your best friend claims that his 100-Dollar
Boom-Box from a local retailer sound as good
as your High-end sound system.
Your sister claims that she hears events, while
you are confident that nothing can be heard.
Your band mate accuses you of changing the
pitch of your guitar with every time you tilt
your wah-wah pedal.
… the scientific study to verify or falsify these claims
leads us to psychoacoustics
Psychoacoustics
Psychoacoustics is the scientific study of
(human) perception of sound.
•Traditionally, Psychoacoustics also includes
the field of speech production.
•It includes applications of
psychoacoustically inspired technical
applications (e.g., audio compression
coders such as mp3).
•Psychoacoustics involves the study of
psychological correlates of physical
acoustical parameters.
Sensation and Perception
Sensation: a mental process (as hearing, seeing,
touching, or smelling) due to immediate bodily
stimulation (it is often distinguished from the
awareness of the process)
Perception: awareness of the environmental
elements through physical sensation (also,
physical sensation interpreted in the context of
experience).
Objective and Subjective
Objective: relating to, or being an object, phenomenon, or condition
in the realm of sensible experience independent of individual
thought and perceptible by all observers
Subjective: relating to or determined by the mind as the subject of
experience or knowledge as conditioned by personal mental
characteristics or states.
Subject in an experiment
(Fig.:Blauert 1997)
Measurement of the
psychophysical function h=f(s)
(Fig.:Blauert 1997)
Correlates between physical and perceived parameters
(Fig.:Blauert 1997)
Physical parameters
Sound pressure level
Frequency
Psychological parameters
Loudness
Pitch
Hypothesis
A hypothesis is a tentative conjecture made in
order to draw out and test its logical or
empirical consequences
Institutional Review Board
http://www.rpi.edu/research/irb/index.html
Approval has to be granted before
psychological experiments can be
conducted.
First Example
• Measurement of the absolute threshold of
hearing (ATH)
The absolute threshold of hearing
(ATH) is the minimum sound pressure
level of a sinusoidal tone at a given
frequency that the average non-impaired
listener can detect in a noiseless
environment.
How can we measure the ATH
• We will need to gain information from
human subjects. E.g., we can present a
pure tone in a noiseless environment to
our subject, and increase the sound
pressure level of the tone until the subject
indicates that he or she perceives the
sinusoidal tone.
Definition Auditory Event
An auditory event is a perceived
acoustic signal, which is in most cases
invoked by a sound pressure wave at
the listener’s ears
Definition Sound Pressure Level
The Sound pressure level (SPL) is a logarithmic measure of the
relative air pressure (root mean square, rms value) of an acoustic
signal p1 to a reference sound pressure (generally: p0 = 20
micropascals (µPa) = 2×10−5 Pascal (Pa):
The unit of the sound pressure level is given in decibels „dB
(SPL)“
Absolute Threshold of Hearing
MAF=minimum audible
field. ATH for
binaural listening in free
field (ISO 389-7)
Resonances
by meatus
and pinna
General 2 dB
difference:
two ears vs.
one.
MAP=minimum audible
pressure. ATH for one
ear headphone
presentation Killion
(1978)
Data are averaged over
many subjects
(Fig. Moore 2004)
Difference between sound pressure at the
eardrum and sound level in free field
(Fig. Moore 2004, Data Shaw 1974)
ATH vs. Duration
I  t  I L   const.
I
Hughes (1946), Garner and Miller (1947)
 
 I  for t  
I  L t
 I L
for t  
with I=threshold intensity,
IL=threshold intensity for a long duration
tone pulse,
t=duration
=integration time of the auditory system
Idea: The auditory system integrates
The sound intensity over time .
Detection is based on minimum energy.

t
ATH vs. Duration
DL is the threshold difference between a 1-s tone and
the tone duration given at the x axis
(Fig.:Terhardt 1998)
I  I L  t  I L   const.
Garner and Miller (1947)
with I=threshold intensity,
IL=threshold intensity for a long duration tone pulse,
t=duration
=integration time of the auditory system
I  I L   t  I L 

I  IL   IL
t
Equation questionable!!!
Clinical Audiogram
(Fig. Moore 2004)
In dB SPL
HL=Hearing Level or
HTL=Hearing Threshold Level,
here the reference level is the
average threshold, pos. # indicate
hearing loss!
Same data in dB HL
Simulated data for a listener
whos ATH is 50 dB below
average across all frequencies
Concept of multiple looks
noise
sine
sine
Level
Varied by ±6 dB
(should matter if
Integration over both
sine tones)
Experiment to test the concept of multiple looks by
Viemeister and Wakefield (1991).
Masker envelope (dashed line), signal envelope (solid
line)
(Fig. Moore 2004)
Concept of multiple looks
The auditory system does not integrate intensity over time,
but it has more opportunities to detect the signal. The data
of Viemeister and Wakefield (1991) support this theory,
because the existance of a second sine tone increased the
detectability of the stimulus, but level variation of the noise
signal in between did not affect listeners’ response.
ATH as function of age
Thresholds of hearing for male (M) and female (W)
subjects between the ages of 20 and 60 (Graph from
Wikipedia.org)