Abstract: A voice detector circuit including a slew-rate limited amplifier at the input thereof so as to reduce the interference with the voice detection process caused by impulse noise. The slew-rate limited amplifier is essentially transparent to audio signals, while providing severe attenuation of impulse noise components. The actual determination of the voice content of the audio signal is provided by comparing the average syllabic-rate content of the impulse noise limited, audio signal with the peak noise content thereof. Additionally, a logarithmic amplifier is included for the purpose of optimizing the separation of the syllabic-rate envelope from the audio signal.

Abstract: An electrically tuned filter arrangement including several tuned filters which may alternatively be coupled to the input and output of the filter arrangement so as to provide the arrangement with different tuning ranges. Each tuned filter has a tuning input to which a capacitive impedance is to be connected for establishing the center tuning frequency of the filter. A capacitor bank is provided including plural individual capacitor elements, and means for coupling any selected combination of the capacitor elements to a capacitive impedance output. This capacitive impedance output is switchably connectable to the tuning inputs of any of the tuned filters.