1/4 inch instrument input - Plug your instrument into this. * Input Gain Level - Regulates the gain stage of the preamplifier and controls the amount of signal available to the unit. * Bass EQ level - 15dB of boost or cut at approximately 30Hz. * Bass Boost - Dynamic Bass boost along Fletcher-Munson Curve * Midrange EQ - Boost or cut middle frequency (as selected by mid-shift)