Music and Hearing Aids

Marshall Chasin, AuD., M.Sc., Reg. CASLPO, Aud(C),
Audiologist,

Musicians' Clinics of Canada, www.musiciansclinics.com
Marshall.Chasin@rogers.com

Hard-of-hearing musicians have long complained about the poor sound quality they experience while playing their instrument or when listening to music through hearing aids. Indeed, many non-musicians also complain of the reduced sound quality of music heard through their personal amplification. A significant electroacoustic parameter is called the "peak input limiting level". In most modern hearing aids, just after the microphone, a limiter exists that prevents anything over 85 dB SPL from getting into the hearing aid. This is quite reasonable for speech since the most intense components of speech are less intense than 85 dB SPL. More intense inputs are therefore not considered to be speech. However, music has levels far in excess of 85 dB SPL and can be as intense as 115 dB-120 dB SPL. Since modern hearing aid microphones can transduce 115 dB SPL, there are few engineering or audiological reasons to set the peak input limiting level at only 85 dB SPL. Following are three sound recordings where the peak input limiting level was set at 115 dB SPL, 105 dB SPL, 96 dB SPL, 92 dB SPL, and finally, for comparison purposes, 115 dB SPL again. Significant distortion exists for peak input limiting levels below 105 dB SPL for music. The song is "Stuck in a moment" by U2. Depending on your internet connection, the audio clips may take some time to load.



Average conversational speech. Each repetition uses a successively lower peak input limiting level, from 115 dB, 105 dB, 96 dB, 92 dB, and finally, 115 dB SPL for comparison purposes. Note that there is no appreciable distortion since the input is only 65 dBA.
<BGSOUND SRC="combination60.mp3">



Music level set at 90 dBA (with peaks about 110 dB SPL). The peak input limiting level drops from 115 dB SPL, to 105 dB, 96 dB, 92 dB and finally back to 115 dB SPL every 11 seconds. There is some distortion as the peak input limiting level drops below 105 dB SPL.
<BGSOUND SRC="combination90.mp3">



Music level set at 100 dBA (with peaks about 120 dB SPL). Again, the peak input limiting level drops from 115 dB SPL, to 105 dB, 96 dB, 92 dB and finally back to 115 dB SPL every 11 seconds. At this input level, some music peaks exceed the capability of the microphone so there is some distortion at all peak input limiting levels. There is appreciable distortion as the peak input limiting level drops below 105 dB SPL.
<BGSOUND SRC="combination100.mp3">



Acknowledgements:

I would like to thank Mead Killion, Norm Matzen, Russ Thoma for the design of the experimental hearing aid; Mark Schmidt for the hearing aid construction; Steve Aiken for the recording of the wave files; my son Shaun Chasin for building this website; and Bill Cole and Jim Kates for many helpful comments during the study. The article that this website is based on appeared in the July 2003 issue of Hearing Journal.