a gated and filtered signal derived from the color subcarrier, called the burst or colorburst, is added to the horizontal blanking interval of each line (excluding lines in the vertical sync interval) as a synchronizing signal and amplitude reference for the chrominance signals. in ntsc composite video, the burst signal is inverted in phase (180° out of phase) from the reference subcarrier. in pal, the phase of the color subcarrier alternates on successive lines.