Abstract: An amplifier uses gain compression techniques to provide linear gain control over a wide dynamic range, and includes an amplifier having input and output legs, a gain controller coupled between the input and output legs of the amplifier, a gain control circuit having an input coupled to the amplifier output leg and output coupled to the gain controller. The gain controller is responsive to a gain control signal to permit continuous gain adjustment of the amplifier. The gain control circuit is configured to compare an output voltage on the amplifier output leg with a predetermined threshold voltage and to generate a gain control signal on the gain control circuit output so as to provide continuous gain adjustment of the amplifier at least when the amplifier output voltage is greater than the threshold voltage. A hearing aid using a single compression amplifier or multiple compression amplifiers to minimize sound distortion and enhance user comfort is also provided.

Abstract: An interface system for communicating between a programmable device, such as a hearing assisting device, and a programmer unit employs a circular shift register and a memory. Upon initialization the memory contents are loaded in the circular shift register and cycled through so that each bit is exposed to the programmer unit for verification or change. After a complete cycle through the shift register the program is fed back to the memory where it is used to control the transfer function of the hearing assisting device. By use of this circular shift register only two connections to the programmer unit are required, thereby minimizing the mechanical size of the connector needed to connect the programmer unit to the hearing assisting device, which may be an in the ear device. A low voltage version of the interface system uses current sources and a high voltage version of the interface system, such as used for a remote controller, uses impedances and a voltage source.

Abstract: A moving-average notch filter with a well-defined phase characteristic for use in eliminating oscillation frequencies in a sound amplification system, wherein this moving-average filter is designed to have an output Y.sub.K in accordance with the system equation ##EQU1## where b.sub.1 are the weighting coefficients, X.sub.K-i are input samples, and K is a constant. This filter may be designed to have a linear phase characteristic. In one embodiment, the location of the notch in the frequency response of the filter may be made to automatically track the drift of an acoustic oscillation frequency.