Fine Tuning Multi-Channel Compression Hearing Instruments

instruments are devices that provide independent non-linear signal processing in many discrete frequency regions. Multichannel capability allows wearers to understand speech better in certain noisy environments. For example, in pediatric fittings, it helps them to monitor their own voice and assists in their speech production. For the dispensing professional, the capabilities of multi-channel instruments allow greater flexibility to fine tune the settings on the hearing instruments to meet the wearer’s needs. The advantage of multi-channel compression processing over single-channel linear processing is exemplified in situations with limited-frequency background noise. A kitchen, for example, can have high-frequency noise due to the clanging of dishes, silverware and pans. Individuals wearing a singlechannel linear hearing instrument in these environments often turn down the volume control of their hearing aid. This user manipulation reduces the intensity of the high frequency noise, but also decreases the audibility of speech in other frequency regions. Multi-channel compression hearing instruments process sounds independently in smaller frequency ranges. One way to envision this is to imagine a two-channel linear hearing instrument with two volume control wheels. This instrument would allow the individual in the kitchen to turn down the volume of the higher-frequency noise and leave the volume of the lower-frequency sounds at the same higher gain setting. While this decreases the audibility of the high-frequency speech sounds, the lowfrequency speech sounds remain intact. Obviously, it would be difficult to place multiple volume control wheels on a hearing instrument and then train the wearer in their proper manipulation. Thus, multichannel hearing instruments require nonlinear processing. Input-output curves are useful in demonstrating the difference between linBy John A. Nelson, PhD