Applied PsychoacousticsLecture 2: Thresholds of Hearing

Jonas Braasch

Your band mate accuses you of changing the pitch of your guitar with every time you tilt your wah-wah pedal.

Your sister claims that she hears events, while you are confident that nothing can be heard.

Your best friend claims that his 100-Dollar Boom-Box from a local retailer sound as good as your High-end sound system.

Your band mate accuses you of changing the pitch of your guitar with every time you tilt your wah-wah pedal.

Your sister claims that she hears events, while you are confident that nothing can be heard.

Your best friend claims that his 100-Dollar Boom-Box from a local retailer sound as good as your High-end sound system.

… 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 Psychological parameters

Sound pressure levelFrequency

LoudnessPitch

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)

MAP=minimum audible pressure. ATH for one ear headphone presentation Killion (1978)

Data are averaged over many subjects

General 2 dB difference: two ears vs. one.

Resonances by meatus and pinna

(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

for t

for t

const.

L

L

L

It

II

ItI Hughes (1946), Garner and Miller (1947)

I

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.

ATH vs. Duration

L is the threshold difference between a 1-s tone and the tone duration given at the x axis

(Fig.:Terhardt 1998)

const. LL ItII

with I=threshold intensity, IL=threshold intensity for a long duration tone pulse, t=duration=integration time of the auditory system

Garner and Miller (1947)

Equation questionable!!!

LL

LL

It

II

ItII

Clinical Audiogram

(Fig. Moore 2004)

HL=Hearing Level orHTL=Hearing Threshold Level,here the reference level is the average threshold, pos. # indicate hearing loss!

In dB SPL Same data in dB HL

Simulated data for a listener whos ATH is 50 dB below average across all frequencies

Concept of multiple looks

(Fig. Moore 2004)

Level Varied by ±6 dB(should matter ifIntegration over both sine tones)

sine sine

noise

Experiment to test the concept of multiple looks by Viemeister and Wakefield (1991).Masker envelope (dashed line), signal envelope (solid line)

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)