5 ms·

> If you watch slow-motion video of a guitar string vibrating, you’ll see a complex, evolving blend of squiggles. These squiggles are the mathematical sum of al

by post-it 7mo ago

> If you watch slow-motion video of a guitar string vibrating, you’ll see a complex, evolving blend of squiggles. These squiggles are the mathematical sum of all of the string’s different harmonics. This is incorrect. If you watch a video like [0], the squiggles aren't real, they're an artifact of a rolling shutter camera. A real slowmo camera will correctly show the entire string vibrating[1]. The rest of the article is correct, but you can't see harmonics happening to the string. [0] https://youtu.be/XOCGb5ZGEV8 https://youtu.be/XOCGb5ZGEV8 [1] https://youtu.be/6sgI7S_G-XI https://youtu.be/6sgI7S_G-XI

RealityVoid 7mo ago
While you're of course righ, in a certain way, the squiggles _are_ a function of the frequnencies that the chords are vibrating at. What you see is the interaction of the two frequencies, your the interaction depends on both frequencies.
throwaway27448 7mo ago
> the squiggles aren't real, they're an artifact of a rolling shutter camera. A real slowmo camera will correctly show the entire string vibrating How do you distinguish vibration from squiggles? To me these seem like the same concept, at the very least over time. The moment simply doesn't matter except to neurotic people without a solid understanding of harmonics and especially of sound.
fuzzfactor 7mo ago
Interestingly, with an oscilloscope you can see the harmonics in all their gory detail :) Actually depending on microphone or instrument interface, you can see stuff that's beyond the range of hearing too. Also, on a low-frequency long-string like an upright bass, if it is bowed at the halfway node, you still hear mainly the fundamental but the second harmonic is naturally emphasized more than usual, and you can also see half the string making its contribution as pictured, with the naked eye.
dahart 7mo ago
Hold on. Your first video is indeed a rolling shutter artifact. But your second video never shows enough of the string to see the harmonics. When you (for example) pluck with a finger on the 12th fret, you absolutely do have a real physical squiggle vibrating in the string, with one node and two antinodes. With a 7th fret harmonic, there are 3 antinodes, with a 5th fret harmonic there are four. There are squiggles, and you can see them with real slowmo.
- engine_y 7mo ago
  Yes, I think that with all these videos what you actually see is aliasing...
- sdeframond 7mo ago
  You can actually see the node with the naked eye. No need for slow mo: the stays put while the rest of the string looks like a blurry mess.
actsasbuffoon 7mo ago
Not sure if I’m misunderstanding your claim. A string does vibrate as the sum of the string’s harmonics. That’s how pinch harmonics work, and they wouldn’t work if that wasn’t the case. You poke a spot where a given harmonic doesn’t vibrate, and that takes energy away from the other harmonics that do need to vibrate at that spot. If we’re just talking about visually being able to see them, I suppose that’s a different question. Maybe on an incredibly low pitched string, or with a strobe light playing at a synced frequency? But in terms of what the string is doing, it is vibrating as the sum of its harmonics.
phkahler 7mo ago
>> but you can't see harmonics happening to the string. But you absolutely can if you rest a finger on a node and pick it, producing primarily the harmonic. You can even see the lesser vibration at the nodes with your eyes.
- kazinator 7mo ago
  If you stretch a rope or chain several meters long, you can simultaneously see the fundamental and first harmonic standing wave.
  - geon 7mo ago
    It is fun to kick a guywire and watch the single pulse travel along the wire, be reflected and come back.
    - DANmode 7mo ago
      > It is fun to kick a guywire Way braver than me!
jMyles 7mo ago
> If you watch a video like [0], the squiggles aren't real, they're an artifact of a rolling shutter camera. ...is this correct? You can say this about any oscillating phenomenon - that doesn't mean it's not 'real'. The "squiggles" are an artifact of the frequency of the string and the scan rate of the rolling shutter. You'll also see artifacting from a global shutter camera, where the "squiggles" will be an artifact of the string frequency and the frame (rather than scan) rate. Or do I misunderstand? I've been playing guitar for 25 years, and it seems to me that I can look at the "squiggles" from a rolling shutter capture of a string and tell you which string it is (and possibly, if I'm having a particularly sharp day, whether it's E or drop-D). I've never tested myself this way - am I certain to fail? :-)
- ses1984 7mo ago
  How could you tell the note by looking at a string? Unless you’re talking by about marking timestamps and measuring the time between peaks. A 42 gauge string tuned to E or D or any other note are going to look basically the same.
  - markrages 7mo ago
    GP is talking about seeing the string oscillations alias against the 30 Hz camera frame rate. I've never tried it.
- tshaddox 7mo ago
  Every pixel of every frame was really captured by the camera from the source, but it’s being played back to you very differently than how the source actually looked. The most obvious example of this would be the wagon-wheel effect, where a spoked wheel can appear to rotate at a different speed and direction than its true rotation when captured by a camera under certain conditions.
alephnil 7mo ago
You would need a frame rate higher than the Nyquist frequency of highest harmonic you want to capture. Since the fundamental frequency of the lowest pitch sting is 83.4 Hz, and you want to capture up to the fifth harmonic (at 83.4 Hz * 5 = 417 Hz) and double that to get the Nyquist frequence, so at least 834 fps. So you would need a high speed camera with 1000 fps to capture the real vibrations.

by post-it 7mo ago

RealityVoid 7mo ago

While you're of course righ, in a certain way, the squiggles _are_ a function of the frequnencies that the chords are vibrating at. What you see is the interaction of the two frequencies, your the interaction depends on both frequencies.

throwaway27448 7mo ago

> the squiggles aren't real, they're an artifact of a rolling shutter camera. A real slowmo camera will correctly show the entire string vibrating How do you distinguish vibration from squiggles? To me these seem like the same concept, at the very least over time. The moment simply doesn't matter except to neurotic people without a solid understanding of harmonics and especially of sound.

fuzzfactor 7mo ago

Interestingly, with an oscilloscope you can see the harmonics in all their gory detail :) Actually depending on microphone or instrument interface, you can see stuff that's beyond the range of hearing too. Also, on a low-frequency long-string like an upright bass, if it is bowed at the halfway node, you still hear mainly the fundamental but the second harmonic is naturally emphasized more than usual, and you can also see half the string making its contribution as pictured, with the naked eye.

dahart 7mo ago

Hold on. Your first video is indeed a rolling shutter artifact. But your second video never shows enough of the string to see the harmonics. When you (for example) pluck with a finger on the 12th fret, you absolutely do have a real physical squiggle vibrating in the string, with one node and two antinodes. With a 7th fret harmonic, there are 3 antinodes, with a 5th fret harmonic there are four. There are squiggles, and you can see them with real slowmo.

engine_y 7mo ago
Yes, I think that with all these videos what you actually see is aliasing...
sdeframond 7mo ago
You can actually see the node with the naked eye. No need for slow mo: the stays put while the rest of the string looks like a blurry mess.

actsasbuffoon 7mo ago

Not sure if I’m misunderstanding your claim. A string does vibrate as the sum of the string’s harmonics. That’s how pinch harmonics work, and they wouldn’t work if that wasn’t the case. You poke a spot where a given harmonic doesn’t vibrate, and that takes energy away from the other harmonics that do need to vibrate at that spot. If we’re just talking about visually being able to see them, I suppose that’s a different question. Maybe on an incredibly low pitched string, or with a strobe light playing at a synced frequency? But in terms of what the string is doing, it is vibrating as the sum of its harmonics.

phkahler 7mo ago

>> but you can't see harmonics happening to the string. But you absolutely can if you rest a finger on a node and pick it, producing primarily the harmonic. You can even see the lesser vibration at the nodes with your eyes.

kazinator 7mo ago
If you stretch a rope or chain several meters long, you can simultaneously see the fundamental and first harmonic standing wave.
- geon 7mo ago
  It is fun to kick a guywire and watch the single pulse travel along the wire, be reflected and come back.
  - DANmode 7mo ago
    > It is fun to kick a guywire Way braver than me!

jMyles 7mo ago

> If you watch a video like [0], the squiggles aren't real, they're an artifact of a rolling shutter camera. ...is this correct? You can say this about any oscillating phenomenon - that doesn't mean it's not 'real'. The "squiggles" are an artifact of the frequency of the string and the scan rate of the rolling shutter. You'll also see artifacting from a global shutter camera, where the "squiggles" will be an artifact of the string frequency and the frame (rather than scan) rate. Or do I misunderstand? I've been playing guitar for 25 years, and it seems to me that I can look at the "squiggles" from a rolling shutter capture of a string and tell you which string it is (and possibly, if I'm having a particularly sharp day, whether it's E or drop-D). I've never tested myself this way - am I certain to fail? :-)

ses1984 7mo ago
How could you tell the note by looking at a string? Unless you’re talking by about marking timestamps and measuring the time between peaks. A 42 gauge string tuned to E or D or any other note are going to look basically the same.
- markrages 7mo ago
  GP is talking about seeing the string oscillations alias against the 30 Hz camera frame rate. I've never tried it.
tshaddox 7mo ago
Every pixel of every frame was really captured by the camera from the source, but it’s being played back to you very differently than how the source actually looked. The most obvious example of this would be the wagon-wheel effect, where a spoked wheel can appear to rotate at a different speed and direction than its true rotation when captured by a camera under certain conditions.

alephnil 7mo ago

You would need a frame rate higher than the Nyquist frequency of highest harmonic you want to capture. Since the fundamental frequency of the lowest pitch sting is 83.4 Hz, and you want to capture up to the fifth harmonic (at 83.4 Hz * 5 = 417 Hz) and double that to get the Nyquist frequence, so at least 834 fps. So you would need a high speed camera with 1000 fps to capture the real vibrations.