Weber-Fechner Law

An approximate psychophysical law relating the degree of response or sensation of a sense organ and the intensity of the stimulus. The law asserts that equal increments of sensation are associated with equal increments of the logarithm of the stimulus, or that the just noticeable difference in any sensation results from a change in the stimulus which bears a constant ratio to the value of the stimulus.

The Weber-Fechner law is applied to the detection of contrast in the problem of visual range, as well as to many other psychophysical problems.


The audibility of differences in the strength of tones of the same frequency goes in stages. It is only when the intensity is increased by at least 10% that a tone is perceived as stronger than another of the same frequency.

The number of intervals of intensity within a 100dB range may be calculated

with ΔI=10%

with the hearing dynamic range of 100dB = 1010

There are approximately 250 intervals of intensity within a 100dB range.

See also: Dynamic Range, Hearing, Knudson′s Law.

Previous PageView links to and from this pageNext Page

Subjects: Noise & Vibration Physics