Why does white on TV make noise?

February 23, 2011 2:04 PM

Why does white on a TV screen cause audible buzzing noise? It's obvious more on an all-white screen, but even small amounts like captions. It seems like it's been this way for decades, through CRT and on to plasma HDTV screens.

Or, alternately, if no one else has noticed this, why can I hear white and how can I use that superpower to fight crime?

posted by davebug to technology (10 answers total)

Does this happen to you when you're watching broadcast or cable television? Or just when you're watching something on DVD or VCR? Because I've had that problem in the past when I had a dvd player using crappy composite video cables.
posted by nushustu at 2:08 PM on February 23, 2011

I notice this, too. Especially from my laptop screen. I've always assumed it's because the screen has to work harder (white light is green, red, and blue all together whereas black is no light) to make white than any other color. But I can't explain any of the science of it.

Either we're both superhuman or everyone can notice this. (If it is superhuman, dibs on not-the-sidekick.)
posted by phunniemee at 2:08 PM on February 23, 2011

I've noticed that on my old TV as well (and have heard it on my parent's new TV). In both cases we had cable TV so maybe it has something to do with the cable TV signal?

I was hoping it meant that the TV was going bad because it actually belongs to my ex husband and I can't wait to go all "Office Space" on its ass and then buy myself a new TV.
posted by MultiFaceted at 2:12 PM on February 23, 2011

I've heard it too and just have assumed its because the components have to work harder to generate the white than all the other colors, kicking it to a higher power level that has a noticeable sound.
posted by msbutah at 2:19 PM on February 23, 2011

It could be interference between the TV's video and audio circuitry. A fully white screen looks a lot like a 60 Hz pulse waveform, and this would be audible. An alternative explanation is that the white screen draws a lot more power, and this taxes the power supply, leading to "dirty" power that in turn affects the audio amplifier.

The root cause is that the components in most TVs are just good enough and no better. You can avoid the problem by using an external amplifier and speaker setup.
posted by kindall at 2:21 PM on February 23, 2011

On a CRT, it's probably doing this because all 3 electron guns are operating at full power.

If the screen is blank, the guns are simply scanning back and forth, and not firing any electrons. Any colors are made up of a combination of the red/green/blue guns operating at varying levels of power. To make white, you mix red, green, and blue and run each gun at full power.

LCDs (ie. flat panel displays and laptops) do not operate in the same manner, and typically the backlight is always turned on and operating at full-power. Showing an all-white screen will require every liquid crystal on the panel to be energized, although that doesn't really require all that much power, and shouldn't create any noise. A white image causes the display to draw barely more power than a black one. If your laptop does this, you're probably noticing GPU "chirping."

Some newer LED-backlit LCD panels can dim portions of their backlights, which allows for reduced energy consumption when displaying a black, partially-black, or dim screen. However, I do not suspect that this has anything to do with our discussion, or would create noise of any sort.
posted by schmod at 2:25 PM on February 23, 2011

Where's the sound coming from? The TV's speakers? Does it go away if you turn the volume down or mute the sound?
posted by exphysicist345 at 2:37 PM on February 23, 2011

What kind of cables is your tv hooked up with ?
posted by majortom1981 at 3:47 PM on February 23, 2011

Yes, I hear it with the speakers muted. It's hdmi cables, to a TiVo that's on cable. I haven't found a blu-ray white screen to test, but I believe it's source-independent.
posted by davebug at 11:24 PM on February 23, 2011

My LCD TV does this, but only when it's on the brighter 'vivid' picture setting. Really annoying.
posted by statolith at 9:21 AM on February 24, 2011