Digital equipment both generates and is highly susceptible to transients and high frequency noise in the 100 KHz range and upward. The generated or received noise, which may be derived from other digital apparatus in the same power system, breaks down into two components. Considering a two line power supply, one component will consist of noise injected into the power current flow and distorts the power current wave form. The other component of the noise is particularly incident to the high speed switching of digital equipment which creates high frequency biases in both conductors simultaneously with respect to ground. The first of these is identified as differential mode noise and the second as common mode noise.