The amount of white noise added to data undergoing analysis for inverse-filter design. An inverse filter tends to build up the higher frequencies in which there is little meaningful data, an undesirable consequence of which is that noise at such frequencies is magnified. The addition of white noise (or what is equivalent, superimposing an impulse or biasing the amplitude-frequency response curve) for filter-design purposes limits the extent to which this can occur. (Note that white noise is not added to the final data, only to the inverse filter design.) See Sheriff and Geldart (1995, 295–297).