The film capacitor has many excellent characteristics, so it is an excellent capacitor. Its main characteristics are as follows: non-polarity, high insulation resistance, excellent frequency characteristics (wide frequency response), and low dielectric loss. Based on the above advantages, film capacitors are widely used in analog circuits. Especially in the part where the signal is cross-connected, capacitors with good frequency characteristics and extremely low dielectric loss must be used to ensure that the signal is transmitted without too much distortion. Among all the plastic film capacitors, polypropylene (PP) capacitors and polystyrene (PS) capacitors are more prominent. Of course, the prices of these two types of capacitors are relatively high. However, in order to improve the sound quality of audio equipment, the parts and materials used have become more and more advanced, and the price is not a more important consideration. Therefore, the frequency and quantity of PP capacitors and PS capacitors used in audio equipment are also increasing.