Acoustic and psychoacoustic benefits of adaptive compression thresholds in hearing aid amplifiers that mimic cochlear function

• Published in: The Journal of the Acoustical Society of America 2001-05, Vol.109 (5_Supplement), p.2355-2355
• Main Authors: Goldstein, Julius L., Valente, Michael, Chamberlain, Roger D.
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4744283

Automatic gain control of linear amplifiers dominates advanced hearing aid design, and has been extensively studied [Levitt et al., IEEE (1980); Dillon, Ear Hear. 17, 287–307 (1996)]. The normal cochlea uses essentially nonlinear, rapidly compressive amplification under efferent control [Kiang et al., Hear. Res. 22, 171–182 (1986); Robles et al., J. Acoust. Soc. Am. 80, 1364–1374 (1986)], whose salient characteristics have been modeled [Goldstein, Hear. Res. 49, 39–60 (1990)] and are presently adopted for multichannel hearing aids. Signal transduction in each channel is linear at low and high sound pressure levels (SPL), and smoothly joined by a compressive range. The transition from linear to compressive response at low SPL is controlled by an adaptive compression threshold, whose quiescent level provides the gain needed for weak sounds. For sustained sounds at higher SPL the compression threshold adapts upwards, providing effectively linear response and better acoustic quality for speech in noise. Pilot psychoacoustic experiments with a design simulation demonstrated that both normal and impaired hearing subjects perceive the improved quality, and comprehend speech in noise at least as well as with advanced hearing aids [Valente et al., J. Am. Acad. Audiol. 9, 342–360 (1998)]. [Work supported by NIDCD.]