Generally speaking , the impedance of a capacitor increases as the frequency of the current passing through it decreases . In other words , a capacitor has infinite impedance at 0 Hz , or DC , and the impedance decreases to 0 as frequency approaches infinity . This has many applications in audio electronics , the two main ones being DC decoupling and filters . By placing a capacitor in the signal path between two sections of an amplifier , you can greatly simplify the design of the circuit at the cost of reduced gain below certain frequencies . Since the capacitor has infinite impedance at DC , no DC current passes through the capacitor . By placing a capacitor in the signal path between two parts of an amplifier , you can treat them as two separate circuits during DC design instead of having to deal with the whole circuit all at once . Capacitors are probably more important in filters , though . Simply put , you can use capacitors in certain configurations to control what happens to current at certain frequencies .