Frequency Discrimination in Noise

Abstract

The relation between frequency discrimination and the ratio of signal-energy to noise-power density (E/No) was investigated at three frequencies—250, 1000, and 4000 cps. On each trial of the experiment, two tones of equa energy were presented one after the other in a background of continuous white noise (32–dB spectrum level). The observers were required to judge whether the first or the second tone had been the higher-frequency tone. The higher-frequency tone was equally likely to precede or follow the lower-frequency tone. Discrimination performance for tones of different frequency separation (ΔF) was measured as the percentage of correct responses in 200 trials. Discrimination performance at all frequencies and all frequency separations increases with increasing E/No until E/No reaches 40 dB. No further increase in performance was apparent with a further increase in E/No of more than 40 dB. The limiting performance levels are not due to amplitude-limiting in the auditory system, since lowering the background-noise level has no effect on the ultimate performance limits. The implications of these data for some models of the auditory process are discussed. [Research supported in part by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]