Analog video recording principles

[DVtyro]

Originally Posted by old_tv_nut

It's the mathematics of what the TIME waveform of the FM signal looks like, and how it is composed of a combination of pure sine waves that individually have a constant frequency and amplitude (the spectrum).

With the extreme case where the luma consists of a high-frequency alternating stripe pattern having peaks and troughs and a certain average level, the TIME waveform of the FM signal shows the FM carrier frequency changing rapidly and repeatedly from low frequency (wide cycles) to high frequency (narrow cycles) representing the troughs and peaks of the luma waveform. Fourier analysis shows that this TIME waveform of the FM signal can be obtained by adding a sine wave with the (constant) average frequency to sine waves of the sideband frequencies. The plot of how much of the average frequency sine wave is there and how much of the sideband sine wave is there is the frequency domain plot of the signal.

Um... Not sure I understood this. Can you explain in layman terms? Say, I have a certain pattern, it is described by the sideband, right? Then I have the same pattern, but brighter, this means that it should look like the previous pattern, but moved to the right? But the frequencies, numerically, will change, they will all move to the right. How the display device will know that it is the same pattern unless it displays the image in relation to the [ever changing] middle frequency?

Thinking about it now, maybe this can be likened to a more simpler case of analog tape recorder. If tape plays faster than normal (so the average frequency is higher) I still hear music, just all notes are shifted, but the intervals between them remain the same. Not sure though, how video patterns correlate to music tones - is it a good enough analogy?