A hearing aid is a device used to help the hard-of-hearing distinguish sounds and converse normally. In the past, hearing aids consisted of a funnel- like amplification cone, called an ear trumpet. Bigger aids used a desk with a built-in amplifier into which a microphone and earphones were plugged; these worked better than passive ear trumpets, however they could be only kept at one place.

Digital hearing aids first came to market in 1987 with two manufacturers introducing hearing aids with digital signal processing (DSP). While high-tech for their time, these hearing aids had little success and were soon abandoned due to their large size and high battery drain.

Nearly a decade later, two separate manufacturers once again introduced digital hearing aids. By this time, the technology had improved so that these hearing aids could be produced in a range of popular styles, from behind-the-ear (BTE) to completely-in-the-canal (CIC). Despite their higher cost, they were well received by clinicians and consumers. This early success, combined with the promise of highly advanced signal processing, ensured that digital hearing aid technology had come of age.

So how far have we come? What is the current "state-of-the art" technology in digital hearing aids? Are digital hearing aids really superior to their analog counterparts? To determine whether digital hearing aids are better for patients, it is important to focus on the superior processing and features of these instruments. Digital hearing aids can't be described as if they are a separate entity from analog hearing aids. "Digital" simply indicates that the analog waveform is converted into a string of numbers for processing; and unfortunately, there is nothing inherently magical about this process. A linear, output-clipping, digital hearing aid could easily be built that would provide sound quality and speech recognition inferior to many analog hearing aids. Therefore, digital isn't superior just because it's digital, but because DSP allows manufacturers to create hearing aids with enhanced processing and features.

The Digital Advantage

Fortunately, for both dispensing audiologists and patients, there are features and advanced signal processing schemes available in current digital hearing aids that do have significant advantages over those found in analog instruments. Potential digital advantages include those related to:

Gain Processing. One of the primary benefits associated with flexible gain-processing schemes is the potential for increased audibility of sounds of interest without discomfort resulting from high intensity sounds. While this is more generally a benefit of compression rather than digital processing per se, the greatly increased flexibility and control of compression processing provided by DSP--such as input signal-specific band dependence, greater numbers of channels, and knee points with lower compression thresholds--can lead to improved audibility with less clinician effort. Expansion, the opposite of compression, has also been introduced in digital hearing aids. This processing can lead to greater listener satisfaction by reducing the intensity of low-level environmental sounds and microphone noise that otherwise may have been annoying to the user.

The most advanced feedback reduction schemes monitor for feedback while the listener is wearing the hearing aid. Moderate feedback is then reduced or eliminated through the use of a cancellation system or notch filtering. DFR can substantially benefit users who experience occasional feedback, such as that associated with jaw movement and close proximity to objects.

Digital Noise Reduction (DNR). This processing is intended to reduce gain, either in the low frequencies or in specific bands, when steady-state signals (noise) are detected. Although research findings supporting the efficacy of DNR systems are mixed, they do indicate that the DNR can work to reduce annoyance and possibly improve speech recognition in the presence of non-fluctuating noise. DNR is sometimes advocated as complementary processing to directional microphones. While directional microphones can reduce the levels of background noise regardless of its temporal content, they are limited to reducing noise from behind or to the sides of the user.

Many theatres and lecture halls are now equipped with assistive listening systems that transmit the sound directly from the stage; audience members can borrow suitable receivers and hear the program without background noise.

Providing good and high quality hearing aid can enhance learning for the hard of hearing and give equality to all. This must be kept in mind while designing schools and other entertainment places. Digital hearing equipment do not cost much and should be acquired to give access to all.