Image quality in old videotapes

[old_tv_nut]

Originally Posted by Rinehart

...They also talked about video tape, and how the image quality of a video cassette--I don't recall if it was VHS or Beta--degraded very quickly as one tape was copied to another, which was then copied to a third. By that point it was just possible to see the image--a BBC 4 ident--but a fourth copy yielded no recognizable image at all. They explained why this was, but it will come as no surprise to anyone here that I didn't understand it...

Don't know what explanation they gave, but part of the problem was that home tape formats had very strong edge enhancement to attempt to make up for the lack of real frequency response, plus noise coring to eliminate tape noise, which also also would lose any low-contrast fine detail. Proper copying decks would turn off this enhancement stuff to try to get a copy as close to the first generation as possible. Otherwise, you'd increase the overdone edge effects on each generation.

Edit: Plus the multiple stages of noise coring and the ever decreasing chroma frequency response would smear everything into looking like a flat area with outlined edges, sort of a smeary "paint by numbers." Also, home formats used comb filters to separate the adjacent track signals and the "color-under" signal from the luminance, so there was increasing vertical smear of the color also as you went from one generation to the next.