Applied PsychoacousticsLecture 2: Basic Measurement Methods, Signal Detection Theory

Jonas Braasch

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)“

Definition Loudness

Loudness is the quality of a sound that is the primary psychological correlate of physical intensity. Loudness is also affected by parameters other than intensity, including: frequency bandwidth and duration.

Scales of Measurement

nominal ordinal interval ratioNon-numeric scale

Scale with greater than, equal and less than attributes, but indeterminate intervals between adjacent scale values

equal intervals between adjacent scale values, but no rationale zero point

Scale has a rationale zero point

e.g., color, gender

e.g., rank order of horse race finalist

e.g., the difference between 1 and 2 is equal to the difference of 101 and 102e.g., Temperature in Fahrenheit

e.g., the ratio of 4 to 8 is equal to the ratio of 8 to 16.

e.g., Temperature in Kelvin.

Measuring loudness in phon

• At 1 kHz, the loudness in phon equals the sound pressure level in dB SPL.

• At all other frequencies the loudness the corresponding dB SPL value is determined by adjusting the level until the loudness is equally high to the reference value at 1kHz (so-called equal loudness curves or Fletcher-Munson curves).

• Loudness measured in Phon is based on an ordinal scale

Measurement Methods

• method of adjustment or constant response– The subject is asked to adjust the stimulus

to a fulfill certain task (e.g., adjust the stimulus to be twice as loud).

• method of constant stimuli – Report on given stimulus (e.g., to what

extent it is louder or less loud then the previous stimulus).

Equal loudness curve

Detection threshold

Just noticeable differences (JNDs)

• Is the smallest value of a stimulus variation (e.g., sound intensity) that we are able to detect.

• A classic example is the work of Fechner measuring the JNDs for lifting different weights