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I am analyzing a series of oscillating data of items that gradually become less "floppy"/oscillatory and I have observed that those items that are less floppy/oscillatory tend to have, what has been explained to me, a prominent "DC component" in their FFT profile plot and their FFT profile looks "cleaner" (maybe because the tall DC component towers over the other peaks). Please see the image below for a representative stiff system: Stiff/not floppy oscillations

Those items that have more floppiness to them on the other hand do not have/show a DC component. Please see the image below for a representative floppy system: Very floppy

How is it that the floppy systems lose their ability to have a DC component, but the stiff systems seem to have nothing but DC components? Would someone please give me some insight as to what this could possibly mean in the physical world? Thanks.

LM

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The "DC Component" of the FFT corresponds to a constant offset or bias in the time domain signal. These are very common both as measurement artifacts or in the physics as well.

Examples: A vertical vibration measurements with an accelerometer will have huge bias: that's just earth's gravity. The actual air pressure of a sound signal has a massive offset: that's the static air pressure. A transistor needs to operate around a bias voltage, etc.

What the underlying cause in your specific data is, I can't tell without having a lot more details about the underlying system/signals and your specific definition of "floppy". In general there is no direct relationship between a bias and mechanical compliance (for a linear spring).

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  • $\begingroup$ Ok, that does make sense. Thanks $\endgroup$ Jul 14 at 3:04

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