Monitor Hum

Today’s NaCreSoMo post isn’t about a Creation but a Distraction.

I have plenty of distractions, of course. Most of my Creations are made at my desk in my bedroom, or perhaps out on the couch in our living room. Right now at 11AM on Sunday I can hear my neighbors playing pop music, it looks like a nice day outside, and I have Facebook open in a background window. Distractions, right?

The one that drives me crazy, though, comes from right here on my desk. My setup at home has my laptop in front of an external LCD; I use the laptop’s keyboard but put most of my windows up on the external display, which is at a more comfortable height. The trouble is, this external display is getting old. And these days, it emits a faint, high-pitched hum, several octaves above comfortable.

(This isn’t the first time I’ve had auditory trouble with some of my equipment. For a while my even-older desktop speakers were very faintly picking up a radio station even at rest. It took me a long time to figure that one out: that I only heard the faint pop music when my own speakers were on.)

Okay, but this is just exaggeration, right? This hum can’t actually be that bad. Maybe it’s all in my head? Well, this morning I realized how I could test that.

This is a spectrogram of a recording of the ambient noise in my room (made with Audacity). I started with my monitor on, then snapped my fingers once (the first vertical line), turned the monitor off, and snapped them a second time. After waiting a bit, I snapped my fingers again, turned the monitor back on, waited for it to settle, and snapped them once more.

There’s a lot of noise down there in the lower frequencies (the y-axis is in Hz), but the high frequencies showed a very clear difference between the monitor off and the monitor on. See that extra horizontal pink line on the top-left and top-right? See how it’s not in the middle?

Things get even clearer if you look at static spectra for the two sections:

These are graphs with frequency (pitch) on the x-axis and amplitude (volume) on the y-axis. (Time doesn’t appear here; this is a rendering of all sounds within a certain time segment, added together.) Again, the lower frequencies don’t match up too well (remember I said my neighbors’ music is coming through the wall?), but starting from about 1,000Hz the shapes on the graphs are essentially the same…except the top graph has a big spike at around 11,000Hz. That’s my monitor hum!

If you want to imagine it for yourself, you can listen to a pure 10,000Hz tone (found with a five-second web search). Then imagine it fainter, a bit higher, not a pure tone, and slightly varying based on what the screen is currently displaying. Aargh!