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.
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.
Maybe I'll get to get it play music (a json with timings and notes would suffice, I suppose?)
You have to calibrate it before it starts playing.
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.
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:
That was a cool hack!!
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.
All video interfaces we use transmit data serially, line by line, pixel by pixel. The bars are 16px tall (black + white) so at 60Hz and 1920×1080px they'll produce a tone with fundamental frequency of 4.05kHz (60Hz × 1080 lines / 16 lines) and harmonics.
(I'm trying to get a recording, but I work in a plant and it's a bit full of white-ish noise...)
Plus: open developer toolbars, find styles for .bars, change margin-bottom and sound changes frequency.
(No sound here)
I also tried test patterns at http://www.lagom.nl/lcd-test/ and http://www.testufo.com/. None of those made caused my screen to make an audible sound.
Though, when scrolling on the site, _something_ (it's not the screen) is making weird noises, almost like the sound when accessing a HDD. I have an SSD though.
I had the same issues with other sites / applications when scrolling in general as well. Even more noticeable with the MacBook Air I had before. Is there any rational explanation for this?
When you are just looking at the screen, and the machine is otherwise idle, the CPU is not doing much, so it goes into low-power low-frequency mode and "sleeps" until some event occurs. When you put fingers on the trackpad and scroll, it sends an "interrupt" to the CPU, telling it that a scroll event has occurred; in a few microseconds the CPU goes from idle to full power to process that scroll event, then goes back to sleep again. The GPU might also be involved in the same way. Every little scroll movement results in an interrupt, so when you are scrolling at a constant rate interrupts occur at a fixed frequency, and the system is going from idle to full power many times a second. The pulses of power draw that this creates, happening at audible frequencies, causes various components like inductors and capacitors to emit sound.