Locate the frequency multiplier tools on the mixer. They should be labeled as "Bass/Low," "Mid" "or High/Treble" on basic mixers. On advanced mixers, they will be labeled in Hertz (Hz) and kiloHertz (Khz).
Play a track through the mixer using an input device (turntable, MP3 player or CD player.)
Adjust the switch that controls the frequency multiplier. This is a bar or lever that alters a particular frequency. Increasing the switch will result in increased levels of that frequency. Decreasing the switch will result in decreased levels. Adjust all switches for their optimum functioning based on the particular song.