Audio voltage signal refers to an AC voltage signal with a frequency range of 20hz ~ 20k Hz (that is, the frequency band of human hearing), and its voltage may change continuously with the waveform in a fixed time, so it is not constant voltage. When the audio voltage signal propagates in the circuit, it may be affected by some circuit components such as capacitors and inductors, and it may be affected by noise, signal attenuation and distortion, resulting in measurement errors. In order to reduce this influence, it is sometimes necessary to introduce filters, amplification circuits and demodulation circuits to improve the measurement accuracy and signal-to-noise ratio. Understanding and processing audio voltage signals requires mastering certain circuit knowledge and measurement skills.