Order cuts are taken from a set of FFTs, each one at a different rpm. The rms level is then found as the Square root of the Sum of the squares of each of the FFT values. Mathematically, if  is the modulus (magnitude) of the  value of the FFT at speed s for  then the rms value at that speed is given by

This takes into account the entire energy at that speed both the order and the non order components, including any noise.

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