Digital Signal Processing: Turning Numbers into Sound

Every time you use your phone or watch a movie you are benefiting from digital signal processing (DSP) of video and audio images.  It is something we all take for granted.  We enjoy the benefits without thinking about the complexity of what is going on behind the scenes. Computer animation used in the movie Toy Story is an example of how digital signal processing provides a different type of creative paintbrush for the visual artist. These computer images are digital images composed of a series of numbers with different values for weight of the line drawn, color, etc. When animators changed the color of a costume or the smile of a character they are actually changing a series of numbers that represented those properties on the computer screen.  Animators don’t have to be mathematicians to appreciate these new tools.  They appreciate being able to achieve special effects faster and more efficiently on the computer and enjoyed applying special effects to the animation that simply could not be done with pen and paper.

These same features of accuracy, efficiency, and unique manipulation have been driving the development of digital audio signal processing in hearing instruments. Since the early 1970s, laboratory researchers could demonstrate the potential of DSP in the laboratory using a room full of equipment, but not many people wanted to haul their hearing aid around in a truck let alone try and find a power outlet. The obstacles to commercial use of this technology in the past have been size of the computer and power consumption.

Madison Connection - Nicolet Project Phoenix

Over fifteen years ago, in 1984, Kurt Hecox, MD, PhD brought together the academic talents of scientists at the University of Wisconsin with the engineering and manufacturing resources of Nicolet Instrument Corporation to form Project Phoenix. Initially funded by the Wisconsin Alumni Research Foundation and the Wisconsin State Department of Development, the project was purchased by Nicolet Instrument Corporation and was successful in bringing its first generation device, the Nicolet Phoenix to market in 1989.  This two-piece device consisted of a pocket computer that was connected to a behind-the-ear hearing instrument.  It offered digital sound processing control over frequency shaping, noise reduction, and loudness control.  Over 200 units were sold, some of which are still in use today.  By 1991, Nicolet’s next generation digital hearing aid, a completely behind-the-ear unit, had passed the prototype stages and was on its way to product release when the project was terminated.  

The Nicolet Phoenix may not have risen from the ashes, but the scientific research and product development served as a foundation for other companies to build upon.  It also shifted the focus of the consumer from cosmetics (remember President Regan’s hearing aid?) to performance. 

DSP Development in Hearing Aids Continues

Leading hearing instrument manufacturers continue to develop new products to meet consumer demands for small size, high performance, and affordable products.  New digital hearing instruments have incorporated the processing power of personal computers into in-the-ear and behind-the-ear hearing instruments. 

DSP hearing instruments are judged by the algorithms or recipes for sound processing that make digital hearing aids unique.  Just like great cooks, engineers and mathematicians guard their recipes carefully because they have worked for years to come up with the right ingredients to make digital hearing aids not only available, but unique performance devices.