Multichannel television sound stereo and surround sound encoder suitable for use with video signals encoded in plural formats

摘要

Method and apparatus for generating a composite audio signal clocked to a selected frequency from left and audio input signals. A video/audio signal generator transmits the left and right audio input signals, together with a video signal having a horizontal synchronization signal embedded therein. If copy protection has not been applied to the video signal, the embedded horizontal synchronization signal will have a frequency of 15.734 KHz. If applied to the video signal, copy protection techniques will shift the frequency of the horizontal synchronization signal. To avoid distortion of the composite audio signal, a switch configured to selectively couple the video signal or a secondary video signal generated by an internal video signal generator to an audio signal processor which generates the composite audio output signal from the left and right audio input signals. Embedded within the secondary video signal is a horizontal synchronization signal having a frequency of 15.734 KHz. Thus, if copy protection features cause the frequency of the signal embedded within the primary video signal to shift, the switch may be used to couple the audio signal processor to the internal video signal generator, thereby ensuring that the composite audio signal will always be clocked to the selected frequency.