A part of seismic recording equipment used to attenuate high-line interference. May consist of bridges that balance the voltage across the input transformers with respect to a center tap at ground potential, the assumption being that voltages with respect to ground are noise. Such bridges usually have two adjustments, for the resistive and reactive components of the high-line-induced voltages. High-line interference is also sometimes reduced with a notch filter which removes a narrow band of frequencies around the high-line frequency. See also humbucking.