Strategy for controlling FM stereo separation and frequency response in noisy reception environments

Abstract

A control for an FM receiver reduces multipath distortion by reducing stereo separation and high frequency response in the demultiplexed signal. The receiver includes an FM detector including a noise detector as well as the signal strength meter for introducing control signals to a separation control and a frequency response control. Unlike the direct input from a noise detector output to the separation and frequency response controls in the prior art, the noise detector output is input through a noise detection manager that generates responses to at least one, and preferably two thresholds of noise detector output. In the preferred embodiment, a stereo separation manager responds to a first threshold of noise and a frequency response manager responds to the second threshold. The frequency response control reduces the high frequency output at the stereo decoder or the audio processor. The respective managers introduce hysteresis by requiring a higher number of noise occurrences, above the said thresholds, to implement separation reduction, frequency response reduction, or a combination of the two, than the number of occurrences required to maintain these reductions. Thus, excessive switching between levels of stereo separation and between levels of high frequency attenuation is avoided.

Dependencies are inferred from the claim text.