The received signals from eddy current testing (ET) sensors are dependent on a large number of variables. These include conductivity, permeability, geometry, and defects in the material being tested, as well as sensor liftoff and orientation. In order to isolate the effects of any one of these properties from the others, multiple inspection frequencies are often used. This paper describes novel adaptations of a standard technique for combining (mixing) the data from multiple frequencies in order to isolate signals of interest. The adaptations were designed for the optimization of signal-to-noise ratio (SNR), where the “signal” is the information of interest and the “noise” is information from other system variables. For example, for detecting cracks in the presence of geometrical changes, the “signal” is the crack information and the “noise” is the information from the geometrical changes.