As long as you stick with microphones and mixers designed for location sound recording and video production, you will not have to worry about impedance matching. The nominal load impedance for a microphone indicates the optimum matching load which utilizes the microphones characteristics to the fullest extent. Impedance is a combination of DC resistance, inductance and capacitance, which act as resistances in AC circuits. An inductive impedance increases with frequency; a capacitance impedance decreases with frequency. Either type introduces a change in phase.