[The status of hearing aid technology from the audiologic viewpoint]

Although hearing aid technology has made considerable progress in the past, some important audiological demands are still unfulfilled. In particular, speech perception in noisy conditions must be improved. Traditional approaches to this fundamental problem, e.g. base cut, open mould fitting, horn equipped ear moulds, external receivers, in the ear hearing aids, directional microphones and audio-input, are discussed, as well as modern concepts of automatic signal processing to improve signal-to-noise (S/N) ratio. The results of a study of speech discrimination with dual channel hearing aids with AGC in the low frequency channel reveal efficient noise reduction in specific S/N situations. However, in the USA self-adaptive noise filter systems in head-worn hearing aids, have proven to be inadequate using the present set of processing parameters. Multichannel and digital signal processing introduce additional unsolved problems into hearing aid fitting.