Resonant frequencies can be accidentally generated by many methods of production. This could be overlapping of instruments, high resonant filters and EQ’s or even poor recordings. Use an EQ with the highest Q (resonant) settings to surgically detect and attenuate resonant frequencies. Slowly sweep through the EQ on solo mode and listen for frequencies that appear to have little to no dynamic movement. These frequencies are generally resonant frequencies that get pinned at a consistent volume and should be controlled. Use just a couple of dB attenuating on these frequencies.
