Choice of Chrominance Subcarrier Frequency in the NTSC Standards

There are a number of considerations which lead to the final choice of the chrominance subcarrier frequency in the NTSC signal. In addition to the considerations given elsewhere it is also desirable to minimize the visibility of the beats between the sound carrier and the chrominance subcarrier. This requires a slight alteration of the nominal field and line rates over those used in monochrome television.