Abstract: In a system for processing stereo signals prior to application to an AM stereo channel information, the signals prior to broadcasting left channel and right channel automatic gain controllers are specially (L+R) gain controlled to maintain monaural loudness and are then followed by a low and high frequency equalizer and filter network. The system next transforms the audio into (L+R) and (L-R) signals and uses a multiband (L+R) and (L-R) peak limiting and clipping system with a variable gain (L-R) "stereo enhancement" amplifier located in the (L-R) path. The (L+R) and (L-R) audio is then applied to final peak clipping bandwidth filters. Finally, the (L+R) and (L-R) audio is transformed back into left and right audio which undergo left and right negative AGC'ing and peak clipping for decoding compatibility.

Abstract: A voltage controlled resistor includes an operational transconductance amplifier (OTA) including first and second linearizing diodes which not only optimize signal-to-noise distortion levels but also represent the AC impedance from the inverting input to ground. The OTA turns on and off in response to the amount of gain control current being supplied thereto. A Darlington transistor is coupled to the output of the OTA for providing a low impedance buffered output. A first resistor provides current flow through the diodes. A feedback resistor supplies and controls bias current to one of the diodes. A third resistor maintains bias to the Darlington pair when the OTA output approaches open circuit output impedance conditions.

Abstract: A circuit for peak limiting an audio signal comprises a first "M" derived filter, a first clipping circuit, a second-order low pass filter, a second clipping circuit and a second "M" derived filter. Each "M" derived filter includes a series resonant shunt leg for eliminating clipping harmonics within selected frequency ranges depending upon the resonant frequency of each shunt leg.