Acoustic reflex, loudness summation, and the critical band

Abstract

As the bandwidth of a sound increases up to the critical bandwidth, loudness remains constant so long as overall intensity is constant. To keep loudness constant at wider bandwidths, intensity must be reduced. Similarly, the minimum intensity required to activate the acoustic reflex (AR) is constant as bandwidth is increased up to a critical value; beyond that value, intensity can be reduced. This critical width is much wider for the AR than for loudness summation. The literature and some new data show that the difference does not arise simply because the AR is measured at signal levels higher than those at which loudness summation is usually measured. Measured at the same high signal levels as needed to activate the AR, the critical band in loudness summation appears to be about two times wider than at lower levels; the ’’critical bandwidth’’ measured for the AR is some four to six times wider. Moreover, the AR shows a strong dependence on the number of components in a multitone complex, whereas loudness summation does not. Also, at very wide bandwidths the AR threshold shows a much larger decrease than would be predicted by the change in loudness. These differences suggest that the AR is not a direct corollary of loudness.Subject Classification: [43]65.22, [43]65.50, [43]65.75.