Static and the color red on TV

Factual Questions
1

One of those lingering questions that just reappeared in the front of my mind…

I saw this most frequently on Nickelodeon, probably because that’s the channel that I most frequently watched (3 kids, you see). At first I thought it was just my TV, but I’ve seen it several times since then, so apparently it’s an actual phenomenon.

Any time something red appeared on the screen, there was a lot of static in the red object. The more red the object was, the more pronounced the static. It wasn’t quite the same kind of static as you see when the TV isn’t getting reception; it was more linear, like silvery dashes.

Is there an explanation for why this happens? I don’t think it was a reception problem - the rest of the picture was fine. It also didn’t seem to be related to the fact that I had satellite - the same thing happened on their grandmother’s digital cable, and I’m pretty sure I’ve seen it on standard cable as well.

2

I’ve had a roughly similar phenomenon… for a while, a screen with a lot of saturated red would make my TV speakers buzz. This was especially obnoxious on TLC, which uses red in all of its promo graphics. And Target ads…ugh…don’t get me started.

It stopped doing it one day, so I assume it was a cable company issue.

3

I notice the same thing when there is a lot of text that appears on screen usually white).

Is that the same thing I wonder?

4

A similar (though different) phenomena I’ve noticed. I do not have cable. I get two local stations, albeit very poorly. The two stations I get come in sorta black and white except for red which shows up as red. No ideas here.

5

On analog TV transmission the sound channel is on an auxilliary sub-carrier just outside the upper frequency of the picture carrier. If there is a picture signal containing large amplitude swings, like from color to white or from one color having a large amplitude difference from an adjacent color, harmonic frequencies will arise. The frequencies are multiples of the basic frequency of the picture signal pulse and if the receiver filtering isn’t all that great they can, and often do, get into the sound channel.

I have no explanation for “static” like steaks in red areas. I’ve never noticed it.

6

Both Trinitrons I’ve bought would bloom and sparkle any area of bright red on the screen.

7

I once asked a friend who had experience operating and maintaining television systems about a similar problem on my cable system. He blamed the cable operator for not properly setting the video modulation levels in their system. Ideally, all the baseband video sources would be adjusted to produce the same output level, and the video modulators would be adjusted to work correctly with that input level. He also said that a similar problem was to blame for the wildly inconsistent audio levels on the channels of the cable system.

8

I forget the exact reasons, but red is susceptible to a lot of artifacts in the North American NTSC video format due to how the red, green and blue color components are mixed together for transmission then un-mixed to light up the appropriate red, green and blue phosphor spots on the picture tube - primarily it’s less-than-perfect circuits and a phenomenon called “red push” that accentuates red.

Ironically, red push is more a problem with HDTV sets as they’ve got more accurate circuitry for decoding the color signal and are all too willing to show the defects in the picture.

9

Um, thanks. I think.

(translation: huh? WhyNot no speak tech. :confused: )

I had a TV once that would go all washed out and the sound would go out when there was more white on the screen than anything else. Very annoying. Never got to watch all of THX1138 'cause of it. (Is that the right number in the title? Too much to do to go look it up.)

10

This is only from recollection, and I’m way, way simplifying things and ignoring other things. Plus, I might have gotten the Y and Cr signals reversed, but this may give you a partial explanation to what’s happening.

The color information for NTSC is transmitted in a format that has three frequency bands, named YCbCr. Y is the luminance (brightness) of the color. Cb is whether the color is more blue or more yellow. Cr is whether the color is more red or more green. Now, think about two ropes, each secured at a wall, where one is being shaken at twice the speed of the other. You’ll see waves something like:



__      __      __      __      __
  \    /  \    /  \    /  \    /  \
  |    |  |    |  |    |  |    |  |
   |  |    |  |    |  |    |  |
   \__/    \__/    \__/    \__/

____            ____            ___
    \          /    \          /
     \        /      \        /
      \      /        \      /
       \____/          \____/

(please excuse the crudeness of ASCII art)

Now, those two ropes kind of represent the frequency bands used by the Y and Cr components. Now, each rope is scaled from 0% to 100% depending upon how bright or red we want the color to be. When we want it dark, the Y rope will still be shaken at the same speed, but the height of the waves on it will be very shallow. When we want it very red, the Cb rope will be still be shaken at the same rate, but the peaks and valleys will be as far apart as possible. Now, to send a signal to the TV to produce a completely red pixel, you would scale the Y rope to about 50% and send the Cb signal at 100%. It turns out that you can “add” these two waves together, producing a wave that looks something like:



__             __               __
  \           /  \             /  \
   \          |   \            |
    \         /    \          /
     \____   |      \____     |
          \  /             \  /
           \/               \/

Basically, it has a gentle slope downwards, and then a sharp spike upwards. This signal will then be separated by your TV’s electronics into the two signals that it’s expecting (along with the Cb component, and there’s an audio frequency band that’s somewhere close to them, too). Now, if the signal that the TV receives is very weak or if the TV’s electronics are sub-standard, it will have difficulty dealing with those sharp spikes upwards, and each signal will sort of “bleed” into each other, so that where there’s supposed to be a constant bright red, you’ll get some speckles of pink, dark red, and white in there, too.

11

Think of the color signal channl as one tank filled with water with vegetable dye in it. The sound channel then will be a tank containing clear water right next to the color tank. There is a lot of agitation and splashing around in the color tank but only gentle ripples in the sound tank. If there are insufficient safeguards between the tanks some of the dyed water from the color tank will splash over into the undyed sound tank.