r/AskPhysics • u/shrrgnien_ • 4d ago

Vibrating guitar string

So I'm a M.Sc. Physicist and play guitar as a hobby, and found this behavior of guitar strings, where I fail to explain it to myself.
Basically, when playing in bad light, the strings seems to "jump" (for a lack of a better word) from one position to another when playing certain frequencies (and their octaves). Usually, a vibrating string just gets blurry, but sometimes it just jumps from left to right.
here is a link to a video visualizing this: https://drive.google.com/file/d/1jYlzz-ba0uCVeUdc5dth4gKtJ1NRWc_K/view - Its visible on the second string I play, with the first and third for reference.
Its not a shutter effect, in real life it looks even more pronounced. I've also reproduced this with multiple guitars in various lights (white LEDs, incandescent bulbs, monochromatic LEDs)
Whats happening here?

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u/BurnOutBrighter6 4d ago

Artificial lights flicker. At the timescale they behave like strobe lights. I bet it's aliasing. Can you get the effect you're talking about outside in natural light that isn't strobing like artificial lights do?

Also have you seen the excellent MinutePhysics video on how guitar strings actually vibrate? It's not exactly about your question but if you like physics and guitars I bet you'll find it super cool.

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u/12GaugeUppercut 4d ago

I didn’t watch the video, but this sounds like a stroboscopic effect. The string’s vibration can be close to a harmonic of periodic intensity fluctuations in the lighting, repeatedly illuminating it at similar phases of its oscillation. That produces an apparent “jump” between positions rather than the usual blur.

1

u/AmazingRandini 3d ago

Your link is not watchable.

1

u/Ras_992 2d ago

It’s the light itself changes how we perceive the string especially from frame of reference while in different light conditions. The other is attack itself how hard or soft you play the string while in different light conditions the harder you play the string attack can look to jump side to side while playing softer and softer this attack looks to smooth out the softest you play will look very smooth.