gms | German Medical Science

Digital hearing aids provide various features to compensate for hearing deficits and beyond [1]. If we restrict the view to hearing-related aspects, there is still a multitude of different features available.

Frequency- and level-specific gain, often referred to as dynamic range compression within hearing aid channels [2], is available to present sounds in a well audible range between hearing threshold and uncomfortable loudness level. In addition, an output limiter serves as a safety feature to prevent users from too loud sounds. For most hearing impairments, the hearing threshold increases with frequency that the auditory dynamic range can become very small or there is even no sensation at higher frequencies. In this case, frequency lowering techniques can be applied which aim to shift acoustic information from higher to lower frequencies and restore audibility in this way.

Audibility is necessary but not always sufficient to gain information from acoustic signals, e.g., in terms of speech intelligibility. Therefore, hearing aids include various features to make sounds better and easier intelligible, or to increase comfort. Gain reduction for noise aims to increase comfort in situations where noise is present only. Noise reduction for speech enhancement can help to enhance speech while noise is simultaneously present. Impulse noise reduction can reduce loud transient noise, and wind noise reduction is helpful outdoors, e.g., on a stormy day, or while riding a bike. Expansion serves as a squelch to reduce microphone noise below hearing threshold, and reverberation suppression can support the user in echoey spaces. If target and interferer signal come from different directions, directional microphones can amplify and highlight the desired signal in a noisy environment. Moreover, directional microphones can be used to partly compensate for the microphone location effect especially of behind-the-ear devices to restore to some extend omnidirectional hearing with open ear. Feedback reduction in hearing aids can help to reduce or completely avoid the situation where feedback causes a whistling noise at the output. Hearing aid programs and adaptive signal processing help to optimize the signal processing for different listening situations, and wireless acoustic inputs can be a great support for hands-free telephone calls (with both ears), wireless music listening, and in situations where the user listens to sounds from a distance, e.g., in a lecture hall, classroom, meeting room, or church.

There are some audiological relevant features that neither restore audibility nor enhance the signal. Data logging can collect data about the individual acoustic environments or wearing behavior to better adjust the hearing aid fitting to individual needs. An acclimatization manager can automatically increase gain over a longer period of time to slowly guide the user towards the intended target which can increase the user’s acceptance of amplification.

Table 1 [Tab. 1]