The Fast Fourier Transform (FFT) is used in vibration analysis. It is well known that Window Filters (Hanning, Flat Top, etc.) can be applied to the time waveform during the batch processing of the FFT, and as a result, decrease the resolution of the FFT. The resolution is decreased by a numerical Window Factor based on the applied filter. It is not well known that the Window Factor
(WF) can also be described as the Equivalent Noise Bandwidth (ENBW) or Noise Power Bandwidth. This paper will explain how to calculate the RMS Energy of the FFT when the WF or ENBW used to process the FFT has a numerical value greater than one.