Abstract: An audio distortion elimination circuit is provided which eliminates the effects of periodic decreases in signal amplitude of an audio signal. A comb filter includes an undelayed signal path, a signal path including a delay line and a combining circuit coupled between a source of audio signals and an audio output circuit. The combining circuit combines the delayed and undelayed audio signals to provide a response for the comb filter which is a function of the delay of the delay line and exhibits periodically recurring points of maximum attenuation at the fundamental frequency of the periodic decreases in signal amplitude and at harmonics thereof. The comb filter may be made adaptive so that comb filtering is provided only during reception of a distorted signal.

Abstract: A noise eliminating system is disclosed for use in a radio receiver including a detector. The system comprises a differentiation circuit for differentiating the signal fed thereto from the detector, a clipper circuit for limiting the amplitude of the signal applied thereto from the differentiation circuit below a clipping level, a clipping level control circuit responsive to the strength of the electric field received in the receiver for varying the clipping level at a rate multiple of the electric field strength, means responsive to the electric field strength for selectively setting the rate at one of a plurality of values, and an integrating circuit for integrating signal fed thereto from the clipper circuit.

Abstract: A diode limiter circuit comprising a low-pass filter for suppressing noise pulses superposed on a demodulated signal and for passing only the noise-suppressed demodulated signal, and a circuit means including limiter diodes whose conduction starting levels are varied according to the waveform of the demodulated signal by superposing the noise-suppressed demodulated signal having passed through the low-pass filter on voltage sources for determining the current conduction starting levels of the limiter diodes to attenuate in a shunting manner the noise pulses exceeding in amplitude of the current conduction starting levels of the limiter diodes.

Abstract: A limiter circuit comprises circuit means for variably controlling a current source for a differential amplifier in accordance with the magnitude of a modulating signal carried by a carrier or a percentage modulation.