[Loudness scaling for narrow band noise and speech signal]

A group of normal-hearing subjects underwent an experimental procedure to obtain estimates of loudness for two narrow band noises, centered at 0.25 and 3 kHz respectively, and meaningful unfiltered speech signals (sentences). Stimuli consisted of 12 intensity levels, spaced equally over the dynamic auditory range. The subjects were asked to associate each level of intensity to one 7 loudness categories. The loudness growth for a noise bands is defined by an exponential function. The loudness growth for the speech signal is better approximated by a linear function. However the mean intensity/loudness function shows two steep portions at the low and high intensities and these are separated by a shallow tract between 55 and 75 dB SPL. The loudness growth for meaningful speech signals--differing from the typical exponential function shown by noise stimuli--seems to confirm the contribution of factors that depend on central auditory organization, most likely operated by the perceptive auditory continuity attributes and the semantic content of the speech signals.