Abstract: An FM radio receiver with a discriminator having connected thereto a plurality of bandpass filters, each tuned to pass a different portion of the audio spectrum from the discriminator, and circuitry connected to the bandpass filters for selecting the filter with the lowest output signal which is an indication of the amplitude of the noise and, hence, the quality of the signal being received by the receiver.

Abstract: An audio signal quality detector connected to receive an audio signal from the discriminator of a radio receiver and including an envelope detector connected to the output of the discriminator and supplying a signal indicative of the envelope of the audio to a resettable valley detector which stores a voltage indicative of the lowest valley applied thereto subsequent to a reset pulse and a sample and hold gate connected to the valley detector for sampling the voltage stored in the valley detector prior to periodic reset pulses applied to the valley detector. Circuitry is also included for inhibiting the operation of the sample and hold gate when there is no output from the valley detector.