Abstract: Extracting a common signal from multiple audio signals may include summing a first signal and a second signal to obtain a first+second signal; subtracting the second signal from the first signal to obtain a first?second signal; transforming the first+second signal and the first?second signal to frequency domain representations; calculating absolute value of the frequency domain representations of the first+second signal and the first?second signal; subtracting the absolute value of the frequency domain representation of the first?second signal from the absolute value of the frequency domain representation of the first+second signal to obtain a difference signal; multiplying the difference signal by the frequency domain representation of the first+second signal to obtain a product signal; dividing the product signal by the absolute value of the frequency domain representation of the first+second signal to obtain a frequency domain representation of the common signal; and transforming the frequency domain repre

Abstract: A signal conditioning circuit for use in broadcasting a composite stereo signal in the 50 hertz to 53 kilohertz range. The signal conditioning circuit includes a filter for attenuating signals above the 53 kilohertz range, a delay circuit to reduce frequency dependent distortion caused by the filter, and an amplitude limiting circuit to reduce filter introduced amplitude distortion. Use of the signal conditioning circuit results in better utilization of the radio station's allocated transmission frequency and allows subchannel carrier authorization (SCA) use of the modulation frequency range above 53 kilohertz.