Abstract: The blades (38) of a gas turbine engine fan rotor (32) are uniquely distributed in the rotor hub (48) so that combination tone noise attributable to one or more physical nonuniformities in the blades is mitigated. The invention recognizes that the frequency spectrum of the combination tone noise includes both decay prone harmonics and decay resistant harmonics and that allocation of acoustic energy into the decay prone harmonics and out of the decay resistant harmonics is effective for mitigating combination tone noise. In particular, the blades are distributed so that the spatial or circumferential spectrum of the physical nonuniformity is dominated by circumferential harmonics whose order is no greater than the order of the highest decay prone harmonic of the combination tone noise spectrum.