Posted on 01/24/2015 9:43:34 PM PST by Swordmaker
No, actually it hasn’t. Keep reading the thread for details.
It’s the same for EVERY stringed instrument. Some of which I’ve been playing for 35 years now...
Well, there is a distinction to be made I think. Video aliasing is from the undersampling of periodic motion and requires multiple frames to exist. Rolling shutter causes a skewed rendering of motion but the motion doesn’t have to be periodic. You can see the effect of rolling shutter in a single frame.
In this video the persistent patterns in the string are from aliasing, and the fact that the patterns are distorted into oddball shapes is from the rolling shutter. Without the rolling shutter, the patterns would have the more typical elliptical shape of resonant modes on a string.
http://digitalcommons.uconn.edu/cgi/viewcontent.cgi?article=1029&context=chem_educ
Sine wave physics.
https://en.m.wikipedia.org/wiki/Waveform
So class, how does a sine wave generator produce a square wave which is a digital phenomena?
Original video synced up various O scope signals and overlayed them on the strings. As I said, heavily doctored.
Dude, calm down. Then check out posts 29 and 24.
Camera artifacts cannot capture what isn’t there in the first place.
It’s a clever video. But it’s fake.
That was awesome and the music was good too!
Camera artifacts *can* create the appearance of things that weren’t there in the first place. Like the bends in the helicopter blade and the weird curve patterns in the airplane propeller seen in the videos posted earlier. Those weren’t there in the first place but they’re certainly there in the video.
BTW, these videos have been discussed at length in other forums and the consensus is that it’s the result of some combination of aliasing and rolling shutter effects. The notion that they’e some sort of photo-shop job is the outlier.
It’s not going to make a sine wave look like a sawtooth or square wave.
Period.
And here I thought he was going to leave it propped up against a wall in a girls locker room..........LOL!
Neat. I have never seen that before.
Very interesting.
There’s nothing there that’s not explained by aliasing and rolling shutter.
Frame rates still apply, Kirkwood. . . because there are still producing frames and rates at which the video is taken. Just because the "shutter" is rolling down the screen hitting lines of pixels sequentially instead of taking the image on all pixels at once is irrelevant. There are still 30 individual frames with isolated images. It is still a video image that will be presented. . . and will be displayed at 30 frames per second at some point. On an iPhone, you can stop the playback at any individual frame and see it. . . ergo, they are individual pictures.
It is just what portion of that image is captured as that frame is built from the sensor and with what degree of accuracy it re-creates the moving object is moving, especially objects moving in directions opposite or counter to the scan line of the CMOS sensor. The slower that motion, the better the CMOS sensor can reproduce it. . . of course that's true of the CCD sensor too.
Dead, the videos from that perspective do show that kind of wave form you show. . . but from the other view the will show the effect shown due to the 30 frames per second rate of the video. There are literally too many of the videos on the internet for it to have been a fake. It is an artifact caused by the combination of a vibrating string interacting with a video's 30 frame rate, whether CMOS or CCD. All that is required is for the string to be in the same position 30 times per second and the wave will show. . . If the string is tuned to any frequency close to a multiple of 30, it will show.
It's a digital camera. . . not analog
Vibrations of strings on a digital camera
One of the commenters on YouTube said:
"This is a cool aliasing effect of the camera's shutter (which probably scans across the image vertically) with the string waves. That's why the effect looks different for horizontal and vertical strings."
Do you realize the amount of work that would be required to "Photoshop" this video for no purpose other than to trick people? It is a real artifact of the CMOS shutter that it will show the actual wave of the sound creation on a string.
I’ll add that all waveforms, including squares and triangles as well as complex shapes, can be formed by adding simple sine waves of various frequencies together.
It’s called the Fourier series, and it’s true in both the analog and digital domains:
http://en.m.wikipedia.org/wiki/Fourier_series
It’s not the direct cause of what’s in the videos but it is in the mix.
Your YouTube video link was done with a Motorola Moto X, which is capable of only 60 frames per second. . . so the slow motion is only half speed. Not too impressive. It uses a CMOS type camera.
Cart before horse.
Unless you are saying the digital camera is producing the square, sawtooth, and square wave forms and superimposing them over the sine wave vibration of the strings.
Which, is not possible. Period.
It’s a photoshop. Occam is in the house.
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