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Comment by drivers99 | Hacker News Reader

"Some surface-mount capacitors exhibit acoustic noise when operated at frequencies in the audio range." [1]

I see that this screen has alternating black and white lines. I count 43 black lines on my monitor. Assuming 60 Hz refresh rate, that is 2580 Hz in terms of the pixels being off or on, which is a perfectly audible frequency. Even with 120 Hz refresh rate, that would be 5160 which is still easily audible. Without knowing anything else, I guess that there may be a capacitor somewhere that is charging and discharging along with the brightness of the screen as it is refreshed from top to bottom, which is causing it to flex in a way that produces an audible noise.

I am curious is Aardwolf can produce different frequencies by varying the width (and therefore the quantity) of black and white lines on the screen. If so, you should be able to play some music on it.

[1] http://www.edn.com/design/components-and-packaging/4364020/R...

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I mocked up a quick JS canvas page that varies the bar width and I do indeed hear the tone changing:

http://thume.ca/screentunes

I also put some ideas on the Github Readme including using feedback from the microphone to calibrate a width->pitch mapping to play music using your screen.

Hey, I forked your repo and added tuning, so that everyone can adjust it for their display

http://genabitu.github.io/screentunes/

Maybe I'll get to get it play music (a json with timings and notes would suffice, I suppose?)

You shouldn't even need the microphone. Assuming that doubling the line frequency doubles the audio frequency, you can play music by just choosing a note to call "A" and varying the frequency from there. It won't be in tune, but that doesn't really matter.

Hey, I have done some work on my fork, and now it plays NYAN CAT (didn't have any better idea...)

http://genabitu.github.io/screentunes/

You have to calibrate it before it starts playing.

Please make a Show HN post. Also prepare for a lot of hits from the random internet. This is amazing.

I can hear the result of this, but it's barely audible, and only near the top of the range, at bar widths thinner than the OP.

I'll have to find some other monitors to test this on. It would be awesome if there were some commplace model that's relatively loud for a wide pitch range. Said model might then be useful for musical hacks in the same vein as driving the stepper motors in old floppy drives.

Hey! For me, this produces sound for the whole range of heights/frequencies! It plays a bit more silent for high frequencies, but for the lowest ones, the sound is quite loud (given it's produced by a screen...) and I think, it could easily go for an even lower pitch. I am using a modified SyncMaster 203B (I replaced some of the electrolytic capacitors after the lighting ceased to work, so that may be it...)

My monitor plays the whole range as well, that's what I calibrated the height sweep to.

Neat. I don't notice anything/much for most of the cycle, but somewhere in the middle I can hear a brief "zwip" rising tone, for part of a second. I happen to have three "identical" monitors, and it's similar on each one, although I believe I can hear the tone for a somewhat longer range on one of them.

I can verify that I hear noise from this on my Macbook Air, faintly, and it also creates a buzzing sound on my iPhone 5s!

I'm on a Macbook Pro. Can't hear anything. Sad :(

Also on an older iPad

I enjoyed that. no noise on my chromebook will try on big monitor in the morning.

That's so cool! I can hear it on my Nexus 5 if I put it right up to my ear!

Awesome! I can hear it perfectly on one monitor at home, but not the other.

This is amazing. Yes, add a song or I will.

If so, you should be able to play some music on it.

Also makes for a nice covert channel... similar tricks with "listening" to the noises a computer makes have been shown to be possible to use for extracting information like encryption keys:

https://news.ycombinator.com/item?id=6927905

Inductors do this as well. The changing magnetic field causes the windings to vibrate, creating an audible sound. The sound my work monitor makes sounds like an inductor to me.

Right--or more commonly the cores of old power transformers will softly buzz at 60 hz.

You'll find it a lot in switching DC-DC converters as well. The pass inductors that help filter out the switching frequency can make quite a bit of noise, especially at higher loads.

My dimmable touch lamp makes an annoying high-pitched sound that is loudest on the dimmest mode. I searched for an explanation and apparently some light bulbs have filaments that are flimsy or light-weight enough that they vibrate audibly.

The power supply on the old Apple II "chirped" when switched off. I always understood it to be the oscillator decaying down from 20 KHz to DC in half a second or so.

Zooming in and out does produce different audible frequencies on my screen.

Something quite different, but it reminds me of Tempest for eliza: http://www.erikyyy.de/tempest/

That was a cool hack!!

I'm getting this as well, on an older dell 2407wfp.

Zooming in (i.e. making the width greater) results in a lower-pitched sound.

Zooming out (i.e. making the width narrower) results in a higher-pitched sound.

Great catch/explanation of this anomaly.

reminds me of how top gear was able to do similar with an F1 Engine https://www.youtube.com/watch?v=5BaR1Kc62Pk

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