Electromagnetic Interference (EMI) is often used interchangeably with Radio-Frequency-Interference (RFI). Technically, EMI refers to the type of energy (electromagnetic), while RFI refers to the frequency range of the noise frequency. Both EMI filters and RFI filters describe unwanted signals (noise) that EMI filters and RFI filters are intended to eliminate. EMI filters and RFI filters consist of a circuit or device containing series inductive (load-bearing) and parallel capacitive (nonload-bearing) components, which provides a low impedance path around the protected circuit for high frequency noise. Filters also attenuate impulses since a Fourier's Analysis of a spike will reveal it is composed of high- frequency waveforms. Filters and surge suppressors when used together thus act synergistically.