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Traditional loudness models have been based on the average energy and the critical band analysis of steady-state sounds. However, most environmental sounds, including speech, are dynamic stimuli, in which the average level [e.g., the root-mean-square (rms) level] does not account for the large temporal fluctuations. The question addressed here was whether two stimuli of the same rms level but different peak levels would produce an equal loudness sensation. A modern adaptive procedure was used to replicate two classic experiments demonstrating that the sensation of "beats" in a two- or three-tone complex resulted in a louder sensation [E. Zwicker and H. Fastl, Psychoacoustics-Facts and Models (Springer-Verlag, Berlin, 1990)]. Two additional experiments were conducted to study exclusively the effects of the temporal envelope on the loudness sensation of dynamic stimuli. Loudness balance was performed by normal-hearing listeners between a white noise and a sinusoidally amplitude-modulated noise in one experiment, and by cochlear implant listeners between two harmonic stimuli of the same magnitude spectra, but different phase spectra, in the other experiment. The results from both experiments showed that, for two stimuli of the same rms level, the stimulus with greater temporal fluctuations sometimes produced a significantly louder sensation, depending on the temporal frequency and overall stimulus level. In normal-hearing listeners, the louder sensation was produced for the amplitude-modulated stimuli with modulation frequencies lower than 400 Hz, and gradually disappeared above 400 Hz, resulting in a low-pass filtering characteristic which bore some similarity to the temporal modulation transfer function. The extent to which loudness was greater was a nonmonotonic function of level in acoustic hearing and a monotonically increasingly function in electric hearing. These results suggest that the loudness sensation of a dynamic stimulus is not limited to a 100-ms temporal integration process, and may be determined jointly by a compression process in the cochlea and an expansion process in the brain. A level-dependent compression scheme that may better restore normal loudness of dynamic stimuli in hearing aids and cochlear implants is proposed.

In normal hearing listeners, a temporally fluctuating sound with modulating frequencies from 4 to 400 Hz was found to be louder than predicted by its averaged power. The louder sensation due to temporal fluctuation was also found to be overall level‐dependent: approaching peak amplitude loudness at a comfortably loud level, becoming less at lower sensation levels, and disappearing at higher levels. If this level‐dependent loudness effect were related to the nonlinear cochlear compression, then it would disappear in cochlear‐impaired listeners because their nonlinear compression is presumably damaged. Three listeners with clinically diagnosed cochlear impairment balanced loudness between white noise and sinusoidally amplitude‐modulated noise. The results showed that the modulated noise was louder for modulating frequencies between 4 and 400 Hz at all three sensation levels, consistent with the hypothesis that the overall level effect on loudness of dynamic stimuli is related to the cochlear compression. Th...

Loudness has been estimated traditionally based on spectral properties of the sound and critical band analysis of the ear: Spectral components add energy within the critical band and add loudness across critical bands. This traditional model is successful in predicting loudness of steady‐state sounds but has not been verified with dynamic sounds like speech. This study conducted three experiments using modern loudness balance procedures to study temporal and spectral factors in loudness sensation. Experiment 1 repeated Zwicker’s two‐tone and three‐tone complex experiment in which frequency and phase differences between tones were varied systematically [Zwicker and Fastl, Psychoacoustics (Springer‐Verlag, 1990), pp. 189–190]. While the results generally were consistent with the traditional model, a deviation occurred for the frequency difference less than 10 Hz, where loudness was affected by the low‐frequency temporal envelope and was greater than that predicted by the energy summation model. To further s...

A pressure regulating ear plug for regulating the rate of change of pressure inside an ear to minimize the pressure differential between the middle ear and a volume of the external ear cavity adjacent the ear drum is made of an ear plug adapted to fit tightly within the external ear cavity with no or minimal air leakage, and disposed within the ear plug is a pressure regulator with a slow leak rate. The pressure regulator is preferably made of a porous ceramic material.