Influence of Monitors on The Resiudal Subcarrier Problem

The presence of residual subcarrier on a studio video circuit produces color errors in the picture seen by the home viewer. Various desighs of receivers and monitors respond to stray subcarrier in different ways, and most studio monitors are capable of virtually ignoring its presence. Furthermore, the signal received by the home viewer is different from that in the studio, due to the operations performed by processing amplifiers. This paper is a non-mathematical tutorial explanation of these effects. It is shown that the monitor characteristic must be taken into account in establishing operating and maintenance techniques to minimize the effects of stray subcarrier. If picture monitors of the type which ignore stray subcarrier are used, residual subcarrier must be detected by other means and eliminated, preferably at the source or alternatively by a downstream processing device. If monitors of the type which display errors due to residual subcarrier are used, extreme care is needed to insure that the monitors are set up and adjusted using test signals free of residual subcarrier. EIA Committee TR4.4.2 is considering a proposal that monitors be equipped with a switch. The effects of residual subcarrier shall be displayed in the "normal" position and suppressed in the alternate position.