This video has a fair few instances where there is an exaggerated wiggling of the guitar strings. I rationalise this by saying its a similar effect to rotoscoping, like where wheels appear to spin backwards as they accelerate in footage. But given the context of music, I remember reading about subharmonics and, besides a particularly niche technique on stringed instruments, they don't really have any real world analogues.

Should these strings appear to oscillate at frequencies related to the subharmonics? If so, what does this say about filming rotating objects and their angular frequency?


In a "consumer grade" digital video camera, the camera does not capture the whole image at once, but "scans" vertically. The artefacts in the video occur because the frequency of the guitar string is close to a multiple of the frame frequency (25 Hz) so the "wavy" artefacts caused by the scanning process appear almost the same on successive frames, and are therefore easily visible as something moving in "slow motion" .

This rolling shutter effect can produce gross distortion of images (see the Wiki link). It has nothing to do with rotoscoping or subharmonics.

Actually subharmonics do have real world significance in many nonlinear dynamic systems - for example the vibration of rotating components with oil-lubricated bearings, in some (usually unwanted and undesirable) circumstances.

This video should make it clear that "what you see isn't real" when the rolling shutter effect is important: https://www.youtube.com/watch?v=EaB9EHeDLSk

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