Abstract: A hearing aid has a sound-receiving microphone from which an incoming signal is supplied to a number of different channels, each channel being allocated to a different frequency range within a total expected range of frequencies for the incoming signal. Each channel includes a circuit for measuring the strength of the signal within the frequency range for that channel and for changing the respective strengths of the signals in the other channels by suppressing weak signal channels in favor of strong signal channels.

Abstract: An apparatus for the transmission of speech, suitable for use in a hearing aid, has an acoustic input transducer followed by a controlled-gain broadband amplifier, which is followed by a parallel circuit of a number of frequency-selecting channels. The frequency-selecting channels divide the broadband output signal of the controlled-gain amplifier into a number of selected frequency channels. A threshold switch is included in each frequency-selecting channel. An acoustic output transducer is supplied with the sum of the output signals of the individual threshold switches.

Abstract: A directional microphone arrangement has a number of discrete microphones each having an electrical output and elements for deriving first and second electrical signals which are 180.degree. out of phase with respect to each other from the outputs of the microphones. A third signal is also derived through differentiation from one of the microphone outputs which is 90.degree. out of phase with respect to one of the first or second signals. All of the first, second and third signals are added in a summing unit, the output of the summing unit forming the output for the arrangement.