Multichannel Nonlinear Frequency Compression: A New Technology for Children with Hearing Loss

Address correspondence to: Susan D. Scollie, Ph.D., National Centre for Audiology, Elborn College, School of Communication Sciences and Disorders, Faculty of Health Sciences, University of Western Ontario, London, Ontario, Canada, N6G 1H1, [email protected] frequency versions of high frequency phonemes during the critical infant, toddler, and preschool years of speech and language acquisition. Two realities collide in our attempts to deliver these high frequency stimuli to the children whom we serve: (1) hearing loss is often greatest in the highest frequencies (Pittman and Stelmachowicz 2003); and (2) hearing aid gain is least in the highest frequencies, which can also be understood as frequencies above the passband of the device. Therefore, we likely cannot provide enough audibility above about 4000 Hz to support consistent acquisition of the high frequency speech sounds by the majority of children who have permanent hearing losses. These problems explain, in part, both recent and not-so-recent interest in signal processing strategies that provide frequency lowering. Early attempts at frequency lowering have been reported in the literature for decades, some with significant reported benefits (Johansson 1961). In recent years, commercially available hearing aids have made a variety of frequency lowering strategies an option for clinical use. These include timevarying whole-band frequency transposition (e.g., the AVR Sonovation Transonic), time-varying frequency transposition of a passband centered on a high frequency peak (e.g., the Widex Inteo), time-varying proportional frequency compression (e.g., the AVR Sonovation Nano) and high-frequency nonlinear frequency compression (e.g., the Phonak Naida). All of these technologies provide frequency lowering. They differ from one another along four dimensions: (1) whether the frequency lowering processing is always on or is time-varying; (2) whether the frequency lowering is achieved by shifting frequencies down (i.e., transposition) versus narrowing the output bandwidth (i.e., compression);