Switch Q1 is an NPN transistor having its collector electrode connected to junction E and its emitter electrode connected to end point G. By controlling, or modulating, the closures of switch Q1, a waveform identical to the ripple on the DC lines 1 and 2 from the DC source (Ir), or from the load (I'r), can be reproduced, and if such occurrence of a synthesized ripple exactly matches the actual lin