and C are respectively a weighted sound pressure level, and A-weighting simulates the human ear's perception of the noise level. The C-weighted sound level is a frequency characteristic that simulates high-intensity noise. Also B-weighted sound level, but rarely used now. Generally expressed in A-weighted sound level, the main instruments used are sound level meters and spectrum analyzers. The results of noise monitoring are used to analyze the current situation and changing trend of noise pollution, and also provide basic data for the planning management and comprehensive improvement of noise pollution. The noise detector uses noise as the measurement of the test signal: the measurement of the noise as the test signal is to use the noise as the test signal to realize the broad-spectrum and dynamic measurement of the system. Generally, Gaussian white noise is used as the test signal, and its probability density function is Gaussian (obeys normal distribution), and its power density spectrum is flat (in the frequency band far wider than the studied frequency).
