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Comment by z-e-r-o | Hacker News Reader

While I totally agree with the moral of this story, I'd like to point some reasons why the visuals of a software might interfere with audio:

1. just check this website: http://thume.ca/screentunes/ there is a large chance that your computer videocard and/or LCD will make a noise on that page

2. when the videocard makes such a noise, it can interfere with the PSU and thus affect the soundcard as well.

3. Thus, it's actually possible that changing a "high-frequency stripy" interface to a solid color will lower the noise-floor on the sound-card a bit.

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I can confirm that. On most computers I could tell what is happening on screen just by listening. Scrolling, video playback, task switching all makes different noises. I have decent headphones and amplifier.

This is a ground loop. Small part of the current returning from CPU to PSU goes through "common ground" connection to the DAC, then through the analog DAC-amp ground conductor, causing some voltage to develop across this connection, and then back to your computer through grounding cables in the walls.

The voltage across DAC-amp ground causes a DC offset seen by the amp (likely less than 1mV). The exact amount of voltage varies in time with CPU power consumption, producing AC that you hear.

You need to eliminate the ground connection between computer and DAC (toslink, USB optoisolator, etc.).

Any external DAC will eliminate this for you.

Nope. I'm running into an external DAC and then a Rega integrated amp. Makes noise her as the bars get smaller. The noise is independent of amplifier volume, including with the amplifier volume all the way down, and even occurs with the amplier and DAC switched OFF. The noise is actually coming from the LCD.

Even decent internal soundcard does.

RE: #1, it definitely made noise on my LCD. It's an older CCFL type backlight, I don't know if that makes a difference but I do know that fluorescent lighting can emit similar sounds.

Can confirm this: Just by listening at the static through my head phones, I can tell what setting my laptop's display brightness is set at.

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