Digital video modulation apparatus

Apparatus for producing, at an output, digital output signals defining the timing and the levels of the peak values, and the timing of the zero values, for a sub-carrier signal amplitude modulated by a modulating signal which comprises means for providing digitized samples of the modulating signal at a rate of twice the frequency of the sub-carrier, selector means for feeding the samples to the output with alternate samples changed in value while preserving their timing relative to the remaining samples, and means for introducing nominally zero signals midway between the samples to define the occurrence of zero levels.