arbilab
Well-known member
I'm one of those who always wants to know 'why'. Here's a 'why' we've all experienced in home technology, though long since retired. Why Beta/VHS looks pretty OK until you try to copy it, then it looks like a half cup of brown poopoo got stirred in.
All small format video records luminance (brightness) and color separately. It all comes in one wire, seemingly all glommed together. Trick being, it's not really glommed, it's combed.
The trick is how they got it all in one wire in the first place. Brightness energy occurs at multiples of (horizontal) line rate, 15,750Hz. Color is encoded at the source to fit between those multiples, where there is a more/less blank space in the spectrum. Very clever.
When you made a recording off TV or camera, the recorder used the same comb to separate brightness and color for processing. Now, there's a little mechanical jitter (jiggle) from the rotating parts when you play it back. Enough to totally destroy color (because it is highly time-dependent), so another very clever arrangement removes the jitter from the color. But not from the brightness. And they both come out the same one wire like they went in.
But not exactly the same. We took the jitter out of color but not out of brightness. Those teeth in the comb? One set (color) is now stationary in time. The other set (brightness) is jiggling. If you want to see the result in Mister Wizard terms, just hold two combs up to a light, hold one stationary and jiggle the other one. You get chaos. The comb filter/separator no longer works.
Remember "S" video? Sort of stood for 'super'; really stood for 'separate'. You used a cable with 2 sets of wires in it. One for brightness, one for color. The two signals weren't combed together and they don't need to get combed apart. S video made pretty good copies. Not everyone noticed though, as S machines sold well above prices for basic ones which were in the low hundred$ by then.
Broadcast machines don't have this limitation. Their much higher speeds allow brightness and color to record together like they come out of the camera. Then both have the mechanical jitter removed together (it's the same jitter for both) by another very clever (also very expensive) device the size of a microwave, a timebase corrector. About the time VHS was coming to an end, their high-end machines ($800-$1400) had a timebase corrector chip in them.
Did I leave anything out? Yes, but anything you were curious about? Like why I wrote this?
Two words, not my favorites: social distancing.
All small format video records luminance (brightness) and color separately. It all comes in one wire, seemingly all glommed together. Trick being, it's not really glommed, it's combed.
The trick is how they got it all in one wire in the first place. Brightness energy occurs at multiples of (horizontal) line rate, 15,750Hz. Color is encoded at the source to fit between those multiples, where there is a more/less blank space in the spectrum. Very clever.
When you made a recording off TV or camera, the recorder used the same comb to separate brightness and color for processing. Now, there's a little mechanical jitter (jiggle) from the rotating parts when you play it back. Enough to totally destroy color (because it is highly time-dependent), so another very clever arrangement removes the jitter from the color. But not from the brightness. And they both come out the same one wire like they went in.
But not exactly the same. We took the jitter out of color but not out of brightness. Those teeth in the comb? One set (color) is now stationary in time. The other set (brightness) is jiggling. If you want to see the result in Mister Wizard terms, just hold two combs up to a light, hold one stationary and jiggle the other one. You get chaos. The comb filter/separator no longer works.
Remember "S" video? Sort of stood for 'super'; really stood for 'separate'. You used a cable with 2 sets of wires in it. One for brightness, one for color. The two signals weren't combed together and they don't need to get combed apart. S video made pretty good copies. Not everyone noticed though, as S machines sold well above prices for basic ones which were in the low hundred$ by then.
Broadcast machines don't have this limitation. Their much higher speeds allow brightness and color to record together like they come out of the camera. Then both have the mechanical jitter removed together (it's the same jitter for both) by another very clever (also very expensive) device the size of a microwave, a timebase corrector. About the time VHS was coming to an end, their high-end machines ($800-$1400) had a timebase corrector chip in them.
Did I leave anything out? Yes, but anything you were curious about? Like why I wrote this?
Two words, not my favorites: social distancing.
