Electroacoustic verification of FM benefits in advanced hearing aid circuitry

Abstract

Miniature FM receivers attached to ear-level hearing aids can provide significant improvements in speech recognition in noisy environments. These receivers are designed to couple to the hearing aid via a boot connection with limited or no adjustment of hearing aid settings. Ideally, the circuitry allows the FM signal to be approximately 10 dB more intense than the typical signal from the hearing aid microphone, allowing for an FM advantage. Furthermore, for intense input levels, the output limiting should not differ for the hearing aid compared to the hearing aid and FM receiver combined, i.e., FM transparency. Following procedures recommended by the American Speech, Language, and Hearing Association, the electroacoustic responses of digital and conventional aids were measured with and without coupling to FM systems at typical conversational input levels and maximum input levels. The rms difference between the electroacoustic responses of the hearing aid alone and coupled to the FM was used to quantify the FM advantage at typical input levels and the FM transparency at high input levels. The finding of great variability in both FM advantage and transparency supports the need for additional fitting controls or design modifications to obtain the maximum FM benefit.