单双音信号频域分析

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clear clc;
close all;
time = 1:1000;
fre1 = 50;
fre2 = 500;
fs = 8000;
sin_signal1 = sin(2*pi*fre1*time/fs);
sin_signal2 = sin(2*pi*fre2*time/fs);
sin_signal = sin_signal1 + sin_signal2;
figure(1);
plot(sin_signal1);
title("单音信号1的时域图");
figure(2);
plot(sin_signal2);
title("单音信号2的时域图");
figure(3);
plot(sin_signal);
title("双音信号的时域图");
figure(4);
plot(abs(fft(sin_signal1)));
title("单音信号1的频域图");
figure(5);
plot(abs(fft(sin_signal2)));
title("单音信号2的频域图");
figure(6);
plot(abs(fft(sin_signal)));
title("双音信号的频域图");
Fs = 8000;  % Sampling Frequency
N    = 128;      % Order
Fc1  = 30;       % First Cutoff Frequency
Fc2  = 60;       % Second Cutoff Frequency
flag = 'scale';  % Sampling Flag
Beta = 0.5;      % Window Parameter
% Create the window vector for the design algorithm.
win = kaiser(N+1, Beta);
% Calculate the coefficients using the FIR1 function.
filter_lowpass  = fir1(N, [Fc1 Fc2]/(Fs/2), 'bandpass', win, flag);
[H,w]=freqz(filter_lowpass);
Hf=abs(H);  %取幅度值实部
% [A1,PS]=mapminmax(Hf)
Hx=angle(H);  %取相位值对应相位角
figure(9)
plot(w*fs/(2*pi),20*log10(Hf))  %幅值变换为分贝单位
title('离散系统幅频特性曲线')
% figure(8)
% plot(w*fs/(2*pi),Hx)
% title('离散系统相频特性曲线')

% figure(7);
% freqz(filter_lowpass);
% title("滤波器频域响应图");
% sin_signal_filter = filter(filter_lowpass, 1, sin_signal);
% figure(8);
% plot(sin_signal_filter);
% title("滤波之后时域图");
% figure(9);
% plot(abs(fft(sin_signal_filter)));
% title("滤波之后频域图");
%