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Wearable Electronics


The sweeping potential of smarter hearing aid design


If hearing aids sounded more natural, millions of people would benefi t. Good news: Now they do. By Lise Henningsen, Head of Audiology, Widex


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lobally, according to the World Health Organization, nearly half a billion people suffer from hearing loss — and number that’s projected to double by 2050. Even so, only about 17 per cent of people who could benefi t from hearing aids use them. It’s been our experience that one important reason is that hearing aids don’t sound natural. Today, engineers have addressed that shortcoming. Most fi rst-time hearing aid users are in their 60s and 70s, and although their hearing problems started years earlier, data shows it can take them, on average, seven years to give hearing technology a try. And when they do, many complain that the sound is “tinny” or otherwise distorted. In fact, sound quality and the “naturalness” of hearing aid sound remain among the most-cited reasons people don’t pursue assistance, despite the strides made in hearing aid innovation over the last decades.


Ironically, the unnaturalness of hearing aid sound is, to a great extent, the byproduct of innovation. When hearing aids went digital, drastic improvements in noise reduction and advanced signal processing came at a price. Originally, hearing aids were designed to compensate for hearing loss and make speech audible again. Of course, the reality was — and remains — that ambient noise and the consequences of hearing loss are variable and listener specifi c.


Today, high-end hearing aids are intelligent. They can process and separate out unwanted noise while simultaneously enhancing nearby speech. Advanced digital hearing aids can even adapt automatically to different listening environments so the wearer doesn’t have to, and they eliminate feedback that might have been associated with analog technology.


They do all this through advanced digital signal processing. But therein lies the rub, and the reason for further innovation to create a more natural sound experience.


Understand the challenge


Taking an analog sound wave, converting it to a digital signal, processing it, then re-converting it back into a sound wave that the ear can perceive, takes time — in most cases 4 to 8 milliseconds. Studies have shown that such a processing delay can adversely affect sound quality. The challenge with a system delay of 4 to 8 milliseconds is simple: If processed sound and unprocessed sound mix in the ear canal of a hearing aid user, the delay has a degrading effect on perceived quality — what’s called the comb fi lter effect. These days, it’s increasingly important to get this effect under control because more hearing aids are fi t with discrete open- or vented-fi t ear sets. As a result, more direct, unprocessed sound passes through the opening around the ear set and mixes with the processed sound from the hearing aid. That’s when the user’s own voice becomes tinny and artifi cial; environmental sounds come out distorted and unusual; and overall, the sound ends up strenuous to listen to over time. For anyone giving hearing aids a try, the effect can be disappointing. And until now, that more natural sound has proven elusive. But smarter, more effi cient processing holds the solution.


42 October 2020 Components in Electronics


Eliminate the delay


The challenge for hearing aid designers is to build a digital signal path with virtually no system delay. Years ago, engineers at Widex developed solutions that achieved what was already the industry’s lowest system delay — around 2 milliseconds. They realized they could do even better. The company’s time domain fi lter bank, along with its 32kHz sampling rate and 16kHz digital bandwidth, results in very high-fi delity sound and offers the perfect backdrop for further tackling the comb-fi lter effect. The solution is an alternate, innovative, high-speed signal pathway through the hearing aid. Widex calls it the ZeroDelay pathway, and it’s ideally suited for people with mild to moderate hearing loss. The new, accelerated pathway results in a processing delay of just .5 milliseconds, effectively eliminating the comb-fi lter effect and the distortion many hearing aid users notice when direct and processed sound come together. In this pathway, all signal processing is adapted to the ZeroDelay design to deliver the best and purest sound quality. Several core functions, such as acoustics stability, adaptive gain control, and enhanced signal-to-noise ratio, still take priority, while others are modifi ed to fi t it to the new paradigm of natural sound design in the faster ZeroDelay pathway.


The two pathways — ZeroDelay and “Classic” — exist side-by- side on the Widex platform. Depending on the needs of the wearer, a hearing care professional can program one or the other as the default mode. The wearer of hearing aids with the two distinct pathways can switch between them based on where they are and what they want to hear, thereby enjoying far greater sound quality and a more natural experience in most situations.


And this could just be the beginning. The development of a ZeroDelay pathway shows us there continues to be room for innovation in recreating natural sound for the millions of people who would benefi t from hearing aids. Engineers are busy exploring new ways to personalize the natural sound of next-generation hearing aids. Their challenge: Having created a more natural sound, how do we tailor it further to users’ preferences, lifestyle, or listening intent? Stay tuned. Lise Henningsen is Global Head of Audiology for Denmark-based Widex. After earning her master’s degree in Speech and Hearing Sciences from the University of Copenhagen, Lise studied audiology at the Central Institute for the Deaf in St Louis Missouri. She has worked in audiological rehabilitation, research and development, and communications since 1990. widex.co.uk


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