Maximal Audible Frequency and Audible Bandwidth
McCreery (2015) reported that “…bandwidth will be limited by a number of factors, not the least of which is the patient's degree of hearing loss. For example, if you have a great hearing aid with a bandwidth going to 9 or 10K for speech, but the patient has a severe hearing loss, it's not likely you'll be able to deliver 9000 Hz to that patient…(and so) audible bandwidth (is) where the average speech spectrum and the peak of the speech spectrum cross the audiogram, from the verification screen….”
Kimlinger et al (2015) report that “the extent to which a listener with hearing loss can benefit from bandwidth expansion is dependent on the audibility of high-frequency cues….” The authors embarked on a study to determine the “maximum audible frequency (MAF) of conventional hearing aids…for different degrees of hearing loss” and to see what spectral changes occur with differing hearing assistant technologies (HATs), and to compare the MAF with the upper limit of the ANSI bandwidth measure.
Eight commercially available hearing aids were selected, three audiometric configurations were evaluated, three HAT products were selected and all measures were gathered on KEMAR. The authors reported the average MAF ranged from 3500 Hz to 8000 Hz and varied across hearing aids, audiometric configurations and stimuli. Of note “The specified upper limit of the ANSI bandwidth was not predictive of the MAF across conditions” They reported most HAT systems did not alter the MAF, although a few did, thus lowering the MAF.
Kimlinger et al concluded that “the MAF of BTEs is dependent on the degree of hearing loss, amplification device, and stimulus input….” “Estimating the MAF (i.e., “where the average speech spectrum and the peak of the speech spectrum cross the audiogram, from the verification screen”) ...can assist clinicians in making decision about which device or configuration of devices provides the greatest access to high-frequency information, as well as whether frequency-lowering technology should be used.”
For More Information, References, and Recommendations
American Academy of Audiology. (2015) Frequency-Lowering and Audible Bandwidth: Interview with Ryan W. McCreery, PhD July 7.
Kimlinger C, McCreery R, Lewis D. (2015) High-Frequency Audibility – The Effects of Audiometric Configuration, Stimulus Type, and Device. Journal of the American Academy of Audiology 26:128-137.