Back to Basics | August 2015 Hearing Review
Up until very recently, our collective amplified heads were submerged in a fog of front-end distortion. Sounds, including music and that of the voices of hard-of-hearing people who wear hearing aids, caused their own hearing aids to be overdriven even before the transmission reached the stage of the brilliantly designed software programming. Even the best of algorithms would function sub-optimally if provided with an initial signal that was less-than-perfect. (For more information on this, see my article1 in the August 2014 Hearing Review special edition about hearing aids and music or go to www.Chasin.ca/distorted_music).
In the last several months the hearing industry has (finally) responded with digital hearing aid analog-to-digital (A/D) converters that can digitize speech and music without distortion. Many manufacturers are now starting to use 24-bit A/D converters rather than the old industry standard 16-bit systems (eg, Unitron’s North platform, Phonak’s Venture platform, and Oticon’s Inium Sense platform). Other manufacturers have implemented some ingenious methods to circumvent the problem. One uses an electronic transformer method (eg, Widex Dream), another uses an analog compressor prior to the A/D converter with digital expansion after digitization (eg, ReSound), and yet another uses a change in the digital register to increase the limited dynamic range to one that is optimized for both speech and music (eg, Bernafon).
Whatever the innovation or the ingenious method of implementing an innovation, for perhaps the first time, sound can get into a hearing aid processing circuitry without distortion. And, with the newer hearing aid microphones that can transduce up to 119 dB SPL (as opposed to last year’s model that could only transduce up to 115 dB SPL), all important stimuli—at virtually all sound levels—can reach the software algorithm and programming stage without distortion. This includes all music, even rock-and-roll, and perhaps just as importantly, the hard-of-hearing person’s own voice at the level of his or her own hearing aids.
Yes, It’s a Big Thing
I would argue that much of the previous research by hearing aid manufacturers into the development of “new and improved” algorithms has been limited by this front-end digitization problem. Algorithms or technologies that have seen limited real-world benefits in the past may now yield significant clinical success.
This reminds me of the history of wide dynamic range compression (WDRC). I am pretty sure that this was from an article that I had read by Mead Killion back in the early 1990s (because I recall reading it while waiting for my young daughter’s soccer practice to end). I have looked everywhere but haven’t been able to find it. However, (and let’s assume that it was from Dr Killion) WDRC was proposed and implemented in the 1970s, but because of the limited bandwidth of hearing aids of that era, it didn’t work. I believe that 1970s WDRC just turned down everything; the manufacturer was Computer Hearing Aids.
With the advent of true wideband receivers in the late 1980s, WDRC was again tried, but this time with great success. This was the 1988 K-AMP designed by Killion and his colleagues. (Incidentally this hearing aid circuit is still available from General Hearing and also in the Bean PSAP.) So this represents a thinly veiled request to revisit many of the hearing aid algorithms of the recent past, but with the newer post-16 bit technology that is now available.
I have made several implicit assumptions that may come back to drown me. One is that each of the newer innovations and newer platforms are equal in their function. I wouldn’t be surprised if indeed this is the case, but that is still yet to be determined. Another assumption is that the various engineering and marketing decisions made by any one manufacturer will not negate the benefits of these new approaches. And the third is that the technical information that has been released to the consuming audiology public is valid (eg, Is a 24-bit platform truly a 24-bit system? Are the instructions only 16-bit?).
Clinically, we have all run into situations where an innovation should work, but doesn’t. Clinically, it doesn’t take long to dismiss something (especially if there is a flood of return for credit hearing aids). Perhaps it’s time for us hearing care professionals to retry what didn’t work last year?
Chasin M. The “best hearing aid” for listening to music: Clinical tricks, major technologies, and software tips. Hearing Review. 2014;21(8):26-28. Available at: https://hearingreview.com/2014/07/best-hearing-aid-listening-music-clinical-tricks-major-technologies-software-tips
Marshall Chasin, AuD, is an audiologist and director of research at the Musicians’ Clinics of Canada, Toronto. He has authored five books, including Hearing Loss in Musicians, The CIC Handbook, and Noise Control—A Primer, and serves on the editorial advisory board of HR. Dr Chasin has guest-edited three special editions of HR on music and hearing loss (August 2014, March 2006, and February 2009), as well as a special edition on hearing conservation (March 2008).
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Original citation for this article: Chasin, M. Back to Basics: Our Heads are Finally Above Water! Hearing Aid Processing Moves Into a New Era. Hearing Review. 2015;22(8):12.?