Tinnitus: Critical Bandwidth-Masking Bands

Abstract

The concept of the critical band was first described in 1937 when Fletcher and Manson (1937) reported the results of an experiment conducted at the Bell Telephone Laboratories in which they used a random noise that had been shown to produce uniform masking throughout the frequency spectrum as the masking stimulus. From the results of this initial experiment, Fletcher (1940) was able to make two important assumptions concerning the masking of pure tones by thermal noise. The first assumption states that only the energy in a narrow band around the test frequency is instrumental in the masking of that pure tone and the energy outside this small band is superfluous. This small band of noise, Fletcher referred to as the ‘critical band’. Secondly, he assumed that at its masked threshold the energy of the tone and overall energy in the critical band were exactly equivalent. Using these assumptions, Fletcher computed critical bandwidths for several different frequencies. He found the critical band to be approximately 63 Hz for a 1000 Hz tone, to remain relatively constant for the lower frequencies, and to increase rather rapidly for high frequencies, reaching a width of about 500 Hz for a tone of 8000 Hz.