Stereophonic television sound transmission system

Abstract

A compatable stereophonic television sound transmission system for transmitting left and right audio signals in conjunction with a television broadcast wherein video information is conveyed on an amplitude-modulated carrier in a frequency channel having defined frequency limits. The system includes at a transmitter location a multiplex generator for generating a composite signal having a first component representative of the sum of the audio signals, a second component comprising an amplitude-modulated suppressed carrier subcarrier signal representative of the difference between the audio signals, and a pilot component representative of the phase and frequency of the suppressed carrier. The composite signal is utilized to frequency-modulate a sound carrier to develop an RF signal component which is added to the television channel at a discrete frequency spacing from the video carrier. The system includes at a receiver location a tuner for converting the transmission channel to an intermediate frequency, a filter for separating the sound signal therefrom, and a detector for deriving the composite signal from the sound signal. The composite signal is demodulated in a stereo demodulating stage to develop the left and right audio signals. Improved noise performance is obtained in the system by applying preemphasis to the left and right audio signals, preemphasis of the composite signal, enhancement of the second composite signal component, and/or Dolby-B processing of the left and right audio signals or to the composite signal. An adapter is shown for utilizing the system for bilingual programming.