critical ratio for masking (Fletcher critical bandwidth)

6.25  critical ratio for masking (Fletcher critical bandwidth). For a pure tone just audible in the presence of a continuous noise of constant spectral density, the ratio of the mean-square sound pressure of the tone to the noise spectral density . Unit, hertz (Hz). See also 6.24 and 6.31.

Annotation 1      By “just audible” it is meant audible in a specified fraction of the trials.

Annotation 2      The term critical ratio for masking avoids confusion with the term critical band. A critical ratio can be converted to a bandwidth. However, the resultant bandwidth will be about 2.5 times smaller than estimates of a critical band obtained by more direct methods.