Abstract: A hearing aid comprising an automatic gain control arrangement which provides an output signal of substantially constant average level. The automatic gain control arrangement has a slow control generator which provides a relatively slow release time and adapts the gain to the average level of the input signal, and a fast generator which provides a relatively fast release time to allow impulsive sounds or transient signals to be accommodated. When a sufficiently loud impulsive sound is received, the fast generator takes control of the gain to avoid discomfort or overloading. The automatic gain control arrangement limits the dynamic range for sound pressure levels above a threshold, such as 60 dB SPL.

Abstract: A hearing aid comprising a microphone whose output signal is split by high and low pass filters and supplied to two channels. Each channel includes a variable gain circuit the outputs of which are mixed and supplied to an earphone. The turnover frequencies of the filters are such that one channel limits the dynamic range of vowels whereas the other channel limits the dynamic range of consonents, thus preventing interaction and masking of consonants by preceding vowels. The intelligibility of speech is thus improved.