A look at the rigorous road a new hearing instrument takes from laboratory to market—and those who make the journey possible.
A hearing instrument is far more than a device that enables the wearer to live more fully in the world of sound. In all its miraculous and miniscule complexity, a hearing instrument represents a wonder of human ingenuity, a concept made concrete after an extended period of research and testing. As a glimpse into Widex’s product development process shows, this does not occur in a haphazard way, and all of the company’s instruments undergo a rigorous and carefully planned journey from laboratory to market.
Philosophy and Practice of Design
Designers and engineers at Widex ApS’ Copenhagen headquarters begin with a vision of what they want, a vision largely determined by the needs of those whom the engineers ultimately serve. “Many years ago when we first came up with a digital hearing aid, we did not say to ourselves ‘We want to have a digital hearing aid,’” says Francis Kuk, PhD (photo), director of audiology, Widex USA, who works at the company’s Chicago research facility. “Instead we asked, ‘What kind of features do we want to have in a hearing aid?’ In essence we defined the needs of hearing-impaired people and the needs of the market. And then we asked, ‘What would be the best way to achieve these goals?’ It was then that we realized that the only way to achieve what we wanted was to have a digital hearing aid.”
Once the product concept is determined, the engineers begin the task of turning it into reality. The process has as much to do with art as it does with engineering. In the early stages of the design, the engineers—some of whom have what are known as “golden ears”—test the product to determine whether or not there is a problem. “We have a certain group of Widex engineers with highly developed listening skills that they can apply to hearing aid sound,” says Kim Nielsen, project manager of Widex’s R & D department in Copenhagen. “This skill enables them to detect even small but often important problems in the design. A lot of people can tell that ‘the sound is not too good’ or ‘something is definitely wrong.’ However, only a few people have the ability to point out in more detail what exactly the problem with the sound is and what might be the cause. These engineers typically have deep insight into hearing aid circuit techniques combined with a privately developed skill for music or musical instruments.” This ability to spot problems in the initial design phase saves costly reengineering or “workarounds” during the later testing process.
But the judgments of these “golden-eared” engineers are not the only ones Widex relies on when testing a product. Hard-of-hearing test subjects from the neighborhoods surrounding the company’s Copenhagen plant are recruited to test the products during the design phase to ensure a new product meets their needs. “We replace our external test personnel on a regular basis to make sure the group of testers are still a group of independent and typical hard-of-hearing persons, each with his or her individual hearing loss characteristic,” says Nielsen. “All test persons are fitted in the Widex R & D facilities by groups of highly skilled engineers and audiologists to ensure the best result and to pinpoint problems at an early stage.” In some cases, the hard-of-hearing subjects drive the design of the product, which sometimes requires the engineering staff to revisit their design. If all of the test subjects dislike a product, the company may even reconsider pursuing it.
After the initial design is approved, the product will move to the field testing phase. In the United States, hard-of-hearing people in the vicinity of Widex USA’s Chicago offices are fitted with the test model. They wear the product home and report on its performance. Once it passes those tests, the product is released to audiologists and other hearing aid dispensers. The company’s premiere instrument, (which has been displayed at the Smithsonian Institution in Washington, DC), was the product of over 7 years of research and development.
The Digital Revolution
What actually goes on inside the hearing aid is the focus of the product testing process, and what goes on is increasingly digital. Digital technology, in fact, is rapidly becoming the standard in the hearing instrument industry, and many companies are committing more of their product lines to this emerging technology.
On the outside, digital hearing aids look much like their analog cousins. The difference is the digital chip inside them. “[Digital processing] preserves the integrity and the nuances of the input better,” says Kuk. “It has less distortion. It has higher fidelity. If your brain can make use of that information, then of course you get more improvement in speech understanding. It starts at the input stage, making everything as accurate as possible, so that the hearing-impaired person has a more comfortable time making sense of the input.”
An analog hearing aid uses a microphone to send a signal through an amplifier to a miniature loudspeaker. The microphone transforms the sound into electrical signals, which are then amplified. The amplified signal is then sent to an output loudspeaker that transforms the electrical signal into a sound signal.
In principle, the digital hearing aid works the same way, taking sound signals and amplifying them. The difference is the way it is achieved. A microprocessor translates the sound signal into a binary digital signal that can be rapidly transformed into a sound signal in real time. “The [digital] approach is much more mathematical, but the end result is very similar,” says Kuk. “It’s driven by mathematical equations. The equations you can use with digital can be more specific to a wider range of sounds, whereas the analog one might not be as specific. The [digital] algorithms are designed to help the ear get the best kind of sounds to process. So if your ear has a 50 dB hearing loss, the algorithm would try to amplify sounds accordingly, so you would get the best sound quality; the best information.”
This means that a digital hearing aid not only can deliver a more complete range of sounds, but also recognize certain sounds over others. One of the company’s instruments, for instance, was designed to recognize the difference between background noise and speech, amplifying speech sound over the background. “The noise reduction algorithm is an advantage of digital signal processing in the sense that the hearing aid looks at the sound that comes into the hearing aid and makes a decision whether it is noise or whether it is speech,” says Kuk. “If it is speech, then you can amplify it by the algorithm. But, if it is noise, it will reduce the amount of amplification the hearing aid provides so you will be more comfortable in a noisy environment. Those things are done automatically by the [digital] hearing aid.”
Digital processing has several key advantages over analog processing. “Digital technology allows a much higher complexity within the practical physical limitations of a modern hearing aid,” says Nielsen. “The digital circuit complexity can be much higher than that of analog circuits without using more power from the battery. In addition to these obvious advantages, digital technology allows the designers total control of circuit-added noise and distortion products since digital circuits can be simulated exactly as they will work in real life. The digital circuits can be designed with completely inaudible circuit noise and distortion. These circuits also have the important advantage of not changing performance due to aging or component tolerances.”
One advantage that has yet to be proved is the longevity of the digital hearing aid over the analog. With fewer parts and its durable digital chip, the digital hearing aid may last longer than the analog’s typical 5-10 years. The only parts that are subject to wear and tear are the microphones and the receivers.
With Widex’s newest product, the Bravo, engineers were faced with the task of providing digital processing at an affordable price. “I think a slogan [for the Bravo] would be ‘digital for everyone,’” says Kuk. “Once we introduced the digital product, we realized the improvement in sound quality. With several high-end digital models available, our challenge was to also provide excellent value with digital performance. So we said digital is the best way to go, but how can we also make it affordable for more people to take advantage of digital signal processing.”
Setting a New Standard
For Kuk, the future is a digital one. “It makes sense for everything to go digital,” he says. “I think the change we see with digital signal processing is like the change from the carbon hearing aid to the transistor. Not only is the sound quality better, the drain is better, the complexity of the processing is better. Even with very small digital hearing aids we are able to do a lot of processing. The result of all this research and development is the ability of wearers to have very natural experiences when it comes to their hearing.”