Effects of Spectral Components, Duration, and Rise Time of Sound on Perceived Noise Level

Laboratory studies were undertaken: (1) to validate, if possible, equal noisiness contours for bands of noise and to extend the range of these contours to higher sound frequencies; (2) to determine the effects of the presence of intense pure‐tone components in wide‐band noise upon judgments of loudness and noisiness; and (3) to equate the effects of rise time, duration, and decay time of a sound upon its judged noisiness. The data indicate that: (1) Presently published equal‐noisiness contours have the proper shape, or nearly so, up to about 6000 cps. An extension of the contours is proposed for use with sounds having higher frequency components. (2) The presence of strong pure‐tone components in a background of broad‐band noise has a much more dramatic effect on judged noisiness than judged loudness. (3) It appears, from a preliminary study, that the trading relation between over‐all duration (⁠$212$ to 20 sec) and peak sound‐pressure level, keeping rise‐ and decay‐time ratios constant is fairly well represented by the “equal energy” rule—i.e., halving the total duration reduces judged noisiness to the same degree as a 3‐dB reduction in sound‐pressure level. The relation of these findings to procedures for the calculation of perceived noise level is discussed. [This work was jointly supported by the National Aeronautics and Space Administration and by the Federal Aviation Agency, under Contract NASr‐58.]