Analog video recording principles

[old_tv_nut]

Regarding the 220% peak white limit:

Before the Freqency Modulation, the luma signal is "pre-emphasized." Thiis means the high frequencies are amplified more than the lower frequencies. Since the high frequencies are involve in producing sharp edges, this means that (in the case of a black to white transition) instead of going from the normal black level to the normal white level, the pre-emphasized luma signal continues to rise above the normal white level for a while and then comes back down to normal white. During playback, the demodulated luma signal is subject to a corresponding de-emphasis that restores the transition to its normal black-to-white transition. Because de-emphasis is reducing the high frequency components of the signal, it also reduces any high frequency noise generated by the tape. A similar technique is used in FM radio broadcasting, and even in recording LP records. Dolby noise reduction and other noise reduction methods go further and use a variable pre-emphasis and de-emphasis to adjust the amount of it depending on whether the audio is soft or loud.

Here is a web site that shows a little-known (these days) video recording system that used variable pre-emphasis, and compares it to VHS's fixed pre-emphasis (Figure 1):
http://www.digiommel.fi/Improving%20...%20Quality.pdf