Last week, in the first of a seven-part series, the problems associated with listening to and playing music with many modern digital hearing aids were discussed. This week’s post discusses some clinical strategies that can improve a hearing aid’s usability with music. It is a common clinical complaint that a person loves their hearing aids for speech (especially in quiet), but have a less-than-stellar view of the sound quality of music.
Here are four things that can be tried or suggested clinically to improve a hearing aid’s function for music. None of these four things are issues of software manipulation- once a music signal is distorted by the front end and A/D technology, nothing, including software manipulation, can improve things. But these four strategies have been shown themselves to be useful.
1. Turn down the volume and increase the hearing aid volume, if necessary:
This strategy derives directly from part 1 of the blog series- simply duck under the doorway. Lower level inputs from a reduced volume on the car radio, an MP3 player attached through the hearing aid, or a home stereo will present the A/D converter with a signal that is within its optimal operating characteristic. Once digitized, the volume (which occurs after the A/D conversion process) may be increased if required. The opposite- turn up the stereo volume- will result in unresolvable distortion.
2. Use (Scotch) tape over the hearing aid microphone(s):
This low-tech approach works wonderfully well. Simply place several layers of tape over the hearing aid microphones and this will reduce the microphone sensitivity to a point where the higher sound level components of music will be within the limited capability of the A/D converter. It’s as if the hearing aid thinks that the input is 10-12 dB lower sound level. If the volume needs to be increased as a result of these layers of tape, this can easily be done, as the volume control is after the A/D conversion process. Some experimentation may be required, as this depends on the gauge of the tape. I find that three to five layers are typically sufficient. The hearing aid user places the tape over their microphone when using it for music and then removes it when listening to speech.
3. Use an assistive listening device (ALD) with its own volume control:
The use of an ALD, such as a microphone plugged into the direct audio input port or coupled inductively, an FM, or an infra-red system can be quite useful, as long as there is a volume control on these devices. In the easiest scenario, plug in an external microphone that disables the hearing aid microphone. Turn down the volume of the ALD microphone (and, if necessary, increase the hearing aid volume to compensate). This, like the above two other strategies, “fools” the hearing aid’s A/D conversion process into thinking that the input is 10-12 dB lower level than the source really is.
4. Remove the hearing aids:
Loud speech can be on the order of 80 dB SPL, but music is inherently higher in sound level than speech. Even quiet music can be on the order of 80-90 dB SPL, with peaks in excess of 110 dB SPL. Because of equal loudness contours, a person with a moderate sensorineural hearing loss may require only several decibels of amplification (if that) even while needing 20-25 dB for speech. Removing the hearing aids will have no deleterious effect for people who have only a mild to moderate sensori-neural hearing loss. And there is no A/D converter to be overdriven!
In next week’s post, we will discuss the first of four hearing aid technologies that the hearing aid industry has provided to resolve this front-end A/D converter-related problem.