February 15, 2011 Audiology

Amplification for Music Lovers

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With the advent of multi-band-wide dynamic range compression in the 1980s, sophisticated directional microphones in the 1990s, and wireless communication with assistive listening and alerting devices in the last several years, one might believe that we have optimal hearing aid technology. To the extent that amplification and assistive devices can help speech, that belief is probably well founded. It is not the case, however, for more intense inputs such as music.

Analog hearing aids of the last several decades, especially with the advent of the K-AMP more than 20 years ago (Killion, 1988), were better for amplifying music than most digital hearing aids today. The problem with listening to louder music with digital hearing aids lies primarily with the analog-to-digital (A/D) conversion stage that is not entailed with analog hearing aids (Chasin & Russo, 2004). Although the digitation process can handle the quieter inputs of speech quite well, it tends to distort the components of music for many listeners.

The "front end" of the hearing aid refers to the technology that occurs before any sound processing, including the microphone, pre-amps, and A/D technology, and tends to be the weak link. Everything in the "front end" is prior to any software processing; if loud music is distorted early on in the hearing aid circuitry, no amount of software adjustment (which doesn't change the operating characteristics of the A/D) can improve music perception. Questions such as "How should I program a hearing aid for a violin player?" are meaningless unless the A/D provides a clear signal.

The best way to think about many modern digital hearing aids is that they have a low doorway into the hearing aid. When one enters a room through a door, the person may hit his or her head on the top of the door if the person is tall (or analogously if the sound is intense) or if an architectural error has positioned the doorway too low. The hearing aid "doorway" is sufficiently high for speech, but too low for music. Striking one's head on the top is the doorway can be compared to how many hearing aids handle most forms of music.

Low-Tech Solutions 

Several low-tech strategies have emerged in the last several years to ameliorate this problem (Chasin, 2010). If a person is listening to a radio or stereo, the simplest solution is to turn down the volume of the music and turn up the volume of the hearing aid to re-establish a comfortable listening level—similar to ducking under a doorway.

Another common strategy is transparent tape. Placing one or two layers of tape over the hearing aid microphone(s) will attenuate the input, "fooling" the A/D into reacting as if the input is well within its operating characteristic. One piece of tape is about 4–5 dB of almost uniform attenuation, up to 6,000 Hz. Two pieces of tape on top of each other are about double that, but provide uniform attenuation only up to about 4,000 Hz. Individuals who go to a concert can place the tape over the microphone(s) of their hearing aids and remove it after the performance.

The balloon is another low-tech strategy for music appreciation used by individuals with hearing impairment. Held in the hands or on the lap during a live performance, the balloon provides an added vibrotactile sensory input that can improve the boost listening enjoyment.

High-Tech Strategies 

Higher-tech innovations also are available and some require minimal cooperation from the hearing aid industry. The use of microphones with up to 12 dB less sensitivity or low-cut (-6 dB/octave) microphones (for those who require amplification only in the higher frequencies) can provide the A/D with a signal that is well within its operating characteristic.

The most high-tech innovations available include software that has been on the market for more than five years that controls the A/D characteristics (Hockley et al., 2010). These software tweaks allow music's more intense inputs to be transmitted through the hearing aid with minimal distortion. Some technologies are based on artificially lowering the inputs just prior to the A/D and then re-establishing them to their initial form—similar to bending down briefly as you go through a low doorway. Other available technologies alter the characteristics of the A/D by sliding the range up and down depending on the nature of the inputs.

Once a distortion-free signal reaches the point of software manipulation, the process is quite straightforward. Music, like speech, requires wide dynamic range compression and a broad bandwidth, but because music is more intense than speech, it typically requires about 6 dB less overall gain and 6 dB lower output sound pressure level-90 (OSPL90) than the "speech channel." Disabling the feedback and noise reduction software also helps to maintain an output that most resembles musical input. Taking care to ensure that the more intense inputs found in music are distortion-free is the greatest challenge.  

Marshall Chasin, AuD, is director of auditory research at Musicians' Clinics of Canada. Contact him at Marshall.Chasin@rogers.com.

cite as: Chasin, M. (2011, February 15). Amplification for Music Lovers. The ASHA Leader.

References

Chasin, M. (2010). Six ways to improve the listening of music through hearing aids, Hearing Journal, 63(9), 27–30.

Chasin, M., & Russo, F. (2004). Hearing aids and music. In T. Ricketts (Ed.), Trends in Amplification, 8(2), 35–48. New York: Westminster Publications.

Hockley, N. S., Bahlmann, F., & Chasin, M. (2010). Hearing instruments to enjoy live music. Hearing Journal, 63(9), 30, 32–33, 36, 38.

Killion, M. C. (1988). An acoustically invisible hearing aid. Hearing Instruments, 39(10), 39–44.



  

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