The input signal may be a voice signal, a modulated telephone signal, an encoded digital signal, a compressed image signal or various sensors. There's no signal. If the amplitude of the input signal is too small or too large, it is generally necessary to amplify or reduce the amplitude of the input signal through an amplification unit and send it to AD for analog-to-digital conversion. If the input signal is noisy, it usually needs a hardware analog filtering unit to filter and shape the signal and send it to AD for analog-to-digital conversion. AD can convert analog signals into digital signals, but it must meet Nyquist sampling theorem, that is, in order to ensure that all information is not lost, the sampling frequency must be higher than twice the highest frequency of the input signal, generally more than five times. The digital signal obtained after AD conversion is input into DSP chip; Then the digital signal is processed by various digital signal algorithms by DSP chip.