非原创，只是将视频中学习到的代码记录一下
需要配合教学视频食用:
%欢快版本
https://www.bilibili.com/video/av17343551
https://www.bilibili.com/video/av17707835
%严肃版本
https://www.bilibili.com/video/av16683579
课程相关代码：
% % 算法工匠 信号源的产生和滤波1 % firdesign.m % author:照着抄的 作者是up主。 % 2018年6月3日 18:12:35 clear ; close all; clc; fc1 = 10; fc2 = 100; fc3 = 450; %三个频率分量 fs = 1000; %采样频率 point_s = 1000; %采样点数 time = [1:point_s]/fs; %时域抽样时间变量 delta_f = 1*fs/point_s; %频率分辨率 sin_s1 = 0.5*sin( 2*pi*fc1*time); sin_s2 = 1.1*sin( 2*pi*fc2*time); sin_s3 = 0.8*sin( 2*pi*fc3*time); sin_s = sin_s1 + sin_s2 + sin_s3; %生成及合成信号 fft_s1 = fft(sin_s); figure(1); subplot(2,1,1); plot(time,sin_s); title(\'原始时域信号\'); f = 0:point_s/2-1; f = f*delta_f; danbianfudu = 2*abs(fft_s1(1:point_s/2 )); subplot(2,1,2); plot(f,danbianfudu); title(\'频域幅度特性\'); %%%%%%滤波处理 %设计低通滤波器，其上限截止频率为fc = 120Hz % wc = fc/(fs/2); N = 128; %滤波器阶数 fc = 120; wc = fc/(fs/2); fir1_lowpass_filter = fir1(N,wc); figure(2); freqz(fir1_lowpass_filter); %查看幅度特性和相位特性(归一化频率) title(\'128阶低通滤波器\'); %实现滤波 filter_sin_s1 = filter(fir1_lowpass_filter,1,sin_s); fft_low_filter = fft(filter_sin_s1); figure(3); subplot(2,1,1); plot(time,filter_sin_s1); title(\'低通滤波后时域波形\'); subplot(2,1,2); danbianfudu = 2*abs(fft_low_filter(1:point_s/2 )); plot(f,danbianfudu); title(\'低通滤波后的频率幅度特性\'); %滤波处理 %设计一个高筒滤波器，截止频率为15Hz fc = 20 ; wc = fc/(fs/2); %视频课件中之所以写0.15，是因为这个例子wc=0.15 对应于75Hz也能滤掉75Hz的，我这里取20Hz fir1_hp_filter = fir1(N,wc,\'high\'); figure(4); freqz(fir1_hp_filter); filter_sin_s2 = filter(fir1_hp_filter,1,sin_s); fft_high_filter = fft(filter_sin_s2); figure(5); subplot(2,1,1); plot(time,filter_sin_s2); title(\'高通滤波后的时域波形\'); subplot(2,1,2); danbianfudu = 2*abs(fft_high_filter(1:point_s/2 )); plot(f,danbianfudu); title(\'高通滤波后的频域幅度特性\');
思考题：如何实现带通滤波器和带阻滤波器？
%带通滤波器 %只让100Hz的通过 %wc1 = 50/(fs/2); %wc2 = 400/(fs/2); fc1 = 50; fc2 = 400; wc1 = fc1 /( fs / 2 ); wc2 = fc2 /( fs / 2 ); fir1_band_pass_filter = fir1(N,[wc1 wc2],\'bandpass\'); %ftype % figure(6); freqz(fir1_band_pass_filter); %实现滤波 fir1_bp_s1 = filter(fir1_band_pass_filter,1,sin_s); fft_bp_filter = fft(fir1_bp_s1); figure(7); subplot(2,1,1); plot(time ,fir1_bp_s1 ); title(\'带通滤波器滤波后波形\'); subplot(2,1,2); danbianfudu = 2*abs(fft_bp_filter(1:point_s/2 )); plot(f,danbianfudu); title(\'带通滤波后的频率幅度特性\'); %带阻滤波器 %只不让100Hz的通过 %wc1 = 50/(fs/2); %wc2 = 400/(fs/2); fc1 = 50; fc2 = 400; wc1 = fc1 /( fs / 2 ); wc2 = fc2 /( fs / 2 ); fir1_band_stop_filter = fir1(N,[wc1 wc2],\'stop\'); %ftype % figure(8); freqz(fir1_band_stop_filter); %实现滤波 fir1_bs_s1 = filter(fir1_band_stop_filter,1,sin_s); fft_bs_filter = fft(fir1_bs_s1); figure(9); subplot(2,1,1); plot(time ,fir1_bs_s1 ); title(\'带阻滤波器滤波后波形\'); subplot(2,1,2); danbianfudu = 2*abs(fft_bs_filter(1:point_s/2 )); plot(f,danbianfudu); title(\'带阻滤波后的频率幅度特性\');