The Crossover Distortion is an analog multi-band distortion effect with a variable crossover.  There are actually four different circuits inside the pedal: two independent cascaded mosfet gain circuits, a continuously variable Linkwitz-Riley crossover, and a discreet output mixer.  The variable crossover splits the input signal at the user-specified frequency, routing the high frequencies to one gain circuit, and the low frequencies to the other.  The highs and lows can then be effected separately, with their own gain and uniquely designed tone controls.  The mixer section recombines the signals prior to output, with ‘Mix’ and ‘Master’ controls to set the balance between the high and low bands and the output volume.