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24 hz sine wave effect |
dj aero
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 Posted: Thu Apr 19, 2012 1:22 pm Post subject: 24 hz sine wave effect |
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This is pretty cool.
Video
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Babaluma
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daverj
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| Posted: Thu Apr 19, 2012 2:32 pm Post subject: |
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Understand that this isn't what it looks like in the room. It is what the camera records because they are running the camera at 24Hz frame rate.
I saw some similar stuff in the early 80s at an art show where they used a strobe light to illuminate the water in a dark space. Then it was what you saw in the room. No camera needed.
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Babaluma
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| Posted: Thu Apr 19, 2012 3:36 pm Post subject: |
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yeah i've seen similar shit with a strobe before, but i didn't realise this wasn't actually what you saw in the room. from the thread title and video i presumed they were playing 24Hz audio waves from the speaker next to the water, and recording the result to digi video regularly.
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jake
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| Posted: Thu Apr 19, 2012 3:38 pm Post subject: |
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| Babaluma wrote: | | yeah i've seen similar shit with a strobe before, but i didn't realise this wasn't actually what you saw in the room. from the thread title and video i presumed they were playing 24Hz audio waves from the speaker next to the water, and recording the result to digi video regularly. |
thats what i thought until you said other wise hahaha
not that good then
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Khyber Pass
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| Posted: Thu Apr 19, 2012 3:41 pm Post subject: |
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Still pretty cool if you ask me. This effect is news to me and as someone who occasionally likes to make a music video, it's got me thinking. Probably lots of cool ways to implement this.
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jonah
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| Posted: Thu Apr 19, 2012 3:44 pm Post subject: |
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What frequency would you have to blast into your eye?
And yeah, I'm sure you could exploit this to make some cool special effects that would take forever to do in post and cost a lot more. It'd be interesting to see this done with targeted blasts of sound. I wonder what this would look like if done to a whole "waterfall"? Would just the center stop? |
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Jason Brock
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| Posted: Thu Apr 19, 2012 4:07 pm Post subject: |
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| jonah wrote: | What frequency would you have to blast into your eye?
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Have you ever seen a car driving next to you and it seems like their wheels are slowly rotating backwards? Somewhere in that range I'd guess. But as far as I can tell your brain's frame rate is variable and if it witnessed freaky shit like that in real life then it would probably adjust and destroy the illusion very quickly.
Edit: also found this interesting on Wikipedia (I had noticed the same thing while eating crunchy potato chips - it vibrates your eyes and creates the effect):
http://en.wikipedia.org/wiki/Wagon-wheel_effect
"Effective stroboscopic presentation by vibrating the eyes"
"Rushton (1967[5]) observed the wagon-wheel effect under continuous illumination while humming. The humming vibrates the eyes in their sockets, effectively creating stroboscopic conditions within the eye. By humming at a frequency of a multiple of the rotation frequency, he was able to stop the rotation. By humming at slightly higher and lower frequencies, he was able to make the rotation reverse slowly and to make the rotation go slowly in the direction of rotation. A similar stroboscopic effect is now commonly observed by people eating crunchy foods, such as carrots, while watching TV. The crunching vibrates the eyes at a multiple of the frame rate of the TV. Besides vibrations of the eyes, the effect can be produced by observing wheels via a vibrating mirror. Rear-view mirrors in vibrating cars can produce the effect."
"Truly continuous illumination"
"The first to observe the wagon-wheel effect under truly continuous illumination (such as from the sun) was Schouten (1967[6]). He distinguished three forms of subjective stroboscopy which he called alpha, beta, and gamma: Alpha stroboscopy occurs at 8-12 cycles per second; the wheel appears to become stationary, although "some sectors [spokes] look as though they are performing a hurdle race over the standing ones" (p. 48). Beta stroboscopy occurs at 30-35 cycles per second: "The distinctness of the pattern has all but disappeared. At times a definite counterrotation is seen of a grayish striped pattern" (pp. 48–49). Gamma stroboscopy occurs at 40-100 cycles per second: "The disk appears almost uniform except that at all sector frequencies a standing grayish pattern is seen ... in a quivery sort of standstill" (pp. 49–50). Schouten interpreted beta stroboscopy, reversed rotation, as consistent with there being Reichardt detectors in the human visual system for encoding motion. Because the spoked wheel patterns he used (radial gratings) are regular, they can strongly stimulate detectors for the true rotation, but also weakly stimulate detectors for the reverse rotation."
"There are two broad theories for the wagon-wheel effect under truly continuous illumination. The first is that human visual perception takes a series of still frames of the visual scene and that movement is perceived much like a movie. The second is Schouten's theory: that moving images are processed by visual detectors sensitive to the true motion and also by detectors sensitive to opposite motion from temporal aliasing. There is evidence for both theories; as of 2011, the debate is not completely settled although the weight of evidence favours the latter." |
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daverj
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| Posted: Thu Apr 19, 2012 5:17 pm Post subject: |
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| jonah wrote: | What frequency would you have to blast into your eye?
And yeah, I'm sure you could exploit this to make some cool special effects that would take forever to do in post and cost a lot more. It'd be interesting to see this done with targeted blasts of sound. I wonder what this would look like if done to a whole "waterfall"? Would just the center stop? |
My guess is that there isn't one. Even with some auto-strobing of the eye, it wouldn't be the same frequency for everybody, and it won't be complete. You would still see the drops continue to fall.
But a strobe can be flashed so fast that you don't perceive it as flashing. If it flashes at around 60Hz or higher (120Hz should be good) your mind should perceive it as continuous light. But if it's a fair amount brighter than the background illumination you'll still get the stop motion from the strobing. So you could create that illusion without it feeling like it is flickering.
And 120Hz is easy to get out of a speaker.
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daverj
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| Posted: Thu Apr 19, 2012 5:37 pm Post subject: |
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The thing I saw was in 1980 at the 15th Annual Avant Garde Festival of New York. It had a tube going sideways with a bunch of holes in it and some kind of mechanism that made a sheet of water drops come out the holes at a specific frequency. The strobe was flashing fast enough that it didn't seem to flicker much, and it made the drops look like they were falling up.
I don't know who the artist was.
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Dr. Sketch-n-Etch
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| Posted: Thu Apr 19, 2012 6:00 pm Post subject: |
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Someone gave me a brilliant little book many years ago called "Soap Bubbles" by Charles Boys. It is full of cool experiments for mischievous young lads to do. One of them is a "water amplifier". If you impart sound vibrations to a stream of falling water (just like in the video), then have the water fall on a drum head or other sort of vibrating membrane, you can transmit the sound using the water as a transmitting medium. If the water falls a long distance, then the reproduced sound can apparently be quite loud, or even destructive.
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Paranormal Patroler
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| Posted: Wed Apr 25, 2012 10:30 pm Post subject: |
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| daverj wrote: | The thing I saw was in 1980 at the 15th Annual Avant Garde Festival of New York. It had a tube going sideways with a bunch of holes in it and some kind of mechanism that made a sheet of water drops come out the holes at a specific frequency. The strobe was flashing fast enough that it didn't seem to flicker much, and it made the drops look like they were falling up.
I don't know who the artist was. |
First thing that came to mind when I saw that video: that would make an awesome (true meaning of the word) installation. Glad to see I'm 30 years late for that.
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Why Adapter
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| Posted: Thu Apr 26, 2012 9:28 am Post subject: |
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There was (maybe still is) an exhibit at the Museum of Science and Industry here in Chi, where there were two streams of water that intersected, seemingly without splashing or interference (under continuous light).
When a stobe came on, though, you could see that the streams were in fact pulses of drops, each drop passing through a gap in the other stream. |
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