中文说明：对PPG信号，也就是脉搏波信号，进行预处理，主要是带通滤波。文件为matlab代码，包括读取数据，设计IIR0.5-5Hz巴特沃斯带通滤波器，显示原信号时域、频域图，滤波前后时域图、滤波前后频域图。
English Description：
PPG signal, that is pulse wave signal, is preprocessed, mainly band-pass filtering. The file is matlab code, including reading data, designing iir0.5-5hz Butterworth band-pass filter, displaying the original signal time domain, frequency domain diagram, time domain diagram before and after filtering, frequency domain diagram before and after filtering.