The Beat Frequency Problem
To understand how the distortion comes about, let us consider an ideal linear process from sampling to display. When a signal is sampled at frequency that is at least double the Nyquist frequency, it can be fully reconstructed by low-pass filtering since the first repeat spectra does not overlap the original baseband spectra. In discrete displays the image signal is not low-pass filtered since the display takes discrete values as input, i.e. the signal displayed contains all the repeat spectra. The proximity of the highest frequency of the baseband signal to the lowest frequency of the first repeat spectra induces the beat frequency pattern. The pattern seen on screen can at times be similar to a Moiré pattern. The Kell factor is the reduction necessary in signal bandwidth such that no beat frequency is perceived by the viewer.
Read more about this topic: Kell Factor
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