How to add audio signals to a video-only switcher?
Audio signals may be added to a video signal in one of two ways: Converting the audio signal to a digitally coded signal, which is inserted into the video signal in the blanking period, where it is not seen on the screen but may be decoded later on. Modulating the audio signal, mixing it with the video signal and, after processing or switching, decoding the audio signal. The advantage of the first system is accuracy and high fidelity of the recovered audio signal, but the price of encoding and decoding is fairly high. The advantage of the second system is simplicity and lower cost, but the mixed signal, which contains high frequency signals, may be severely degraded by simple switchers and DAs that limit the transmitted video bandwidth. Since DAs and switchers now usually have large bandwidth due to the nature of the signals available in a studio, the second system is most suitable.
