Despite the rapid development in hearing aid technology since the introduction of DSP in 1996, the limitations of current devices are still recognized,1-6 with significant numbers of hearing aid wearers continuing to express dissatisfaction in key fields such as clarity, sound naturalism, ability to hear soft sounds, and degree of acoustic feedback/buzzing/whistling experienced (dissatisfaction rates above 20% are reported for several fields).
1,6 The imperfect nature of current BTE digital hearing aids is not surprising given that every amplifier has response limitations (e.g., in relation to frequency or bandwidth, phase and slew-rate), and such limitations are to be especially expected within the confines of miniaturization. Additionally, the close proximity between speaker and amplifier for digital hearing aids makes adverse acoustic feedback effects inherently likely which in turn necessitates feedback countering technology, the effectiveness of which can vary for even the most sophisticated of digital hearing aids, depending on the environmental circumstance. Indeed, many aspects of a comprehensive 1996 review4 into acoustic feedback and other audible artifacts for hearing aids remain relevant for today’s devices.
Thus, while current BTE and other digital hearing aids are technologically impressive, generally perform well and help hearing impaired people worldwide, their perfect performance cannot be expected, with the not uncommon complaint made by users, that the device amplifies sounds to an adequate level of perceived loudness yet does not meet expectations of improved audible clarity, involving a complexity of issues that are difficult to address within the above-identified miniaturization confines.