## Order Cuts And Overall Level

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 $x_{ks}$ is the modulus (magnitude) of the $k^{th}$ value of the FFT at speed s for $k = 1,\dots,N-1$ then the rms value at that speed is given by

$rms_s = \sqrt{\sum_{k=0}^{N-1}{x_{ks} ^2}}$

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