# Knudson′s Law

The difference in frequency between pure tones of equal strength and of which the difference in pitch is just perceptible is defined by Knudson’s law as approximately:

If we apply this law to see how many tones whose frequency difference is audible occur in the audible frequency range of 20Hz to 20000Hz.

If there are z tones

substituting Δf/f and taking the log gives

this can then be rearranged to give

There are 2000 tones whose frequency difference is audible in the audible frequency range.

**See also: **Ear, Hearing, Weber-Fechner Law.

**Subjects: ** Audio Noise & Vibration