Scan Velocity Modulation, what does it do? (1 Viewer)

[Jonathan Dagmar]

Of course I have heard that VSM is bad, and evidently even JVC knows this, since the "theatre" mode on my 27" I'art automatically turns it off (and incidently provides to my eye very accurate colour, contrast and brightness).

But what exactly does it do? I turnd my tv into "standard" mode, which has awful colour, but has VSM on by default, and then flip VSM on and off while viewing CNN, and could notice almost no difference whatsoever.

So what exactly is it supposed to do, and why can't I see the effect?

 

[Craig Robertson]

it slows down the scanning of the electron beam across the screen where the portion of the scan line is bright and speeds it up where it is dark. when it's slow, the beam strikes the inside of the tube face for a longer time making it brighter, and the reverse when it is fast. this creates a greater difference between dark and light portions of the screen.

 

[Jonathan Dagmar]

oh thanks, but I guess I wasn't clear enough. What I wanted to know is what this does that is so "bad" that some people refer to "picture destroying VSM".

 

[Scott Kimball]

One effect of VSM is that it artificially "hardens" transitions from light to dark... in essence, it's similar to edge enhancement.

Look closely at defined edges while this "feature" is turned on, and you'll very likely see artifacts similar to what you see with edge enhancement.

You can get similar results by cranking the sharpness control way up.

-Scott