This report provides the technical rationale for revision of a chart developed by Fidell, Pearsons, and Bennett (1972). This chart expresses the relationships between signal-to-noise ratio and frequency that govern detectability of acoustic signals by human observers. The chart permits a user: (1) to predict the frequency region of a spectrum that is most detectable in any given ambient noise background; (2) to quantify the degree of detectability of the signal in question; and (3) to estimate reduction in signal-to-noise ratio necessary to render the signal undetectable.
