What kind of wave analysis is it?

I have seen some image of analyzing vibration for sound wave, which will form a polygon with 7 corners, just like a flower shape on some engineer's tools, rather than a sine wave. If any of amplitude, frequency, ... adjust, then number of corners will change. Do you have any idea on those analysis? why does the vibration show a polygon with 7 corners? How do the number of corners being interpreted in term of vibration?

Does anyone have any suggestions

Thank you very much

Eric
What kind of wave analysis is it?
I do not believe there are any interferometric devices that display a heptagon.

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