Matlab-对wav音频文件AM调制及解调

1.读取wav音乐文件

% 读取音频文件
filename = 'jay.wav';
[sound_data, fs] = audioread(filename);  % 9507502x2 44100
sound_data_1 =  sound_data(:, 1);
sound_data_1 = sound_data_1';             % 转置

sound_data有两列，因为此音乐文件有两个通道，音频采样率为44100；

这里只使用其中一个通道数据；

将多行数据转置为单行数据，方便后续调制

2.调制

% 调制参数
carrier_freq = 1000;    % 载波频率
modulation_index = 0.5; % 调制指数
dc = 1;                 % 直流偏置

% 创建载波信号
t = (0:length(sound_data_1)-1) / fs;
carrier = cos(2*pi*carrier_freq*t);

% 进行AM调制
sound_data_1 = dc + modulation_index*sound_data_1;  %直流偏置，乘以调制指数在偏置    
modulated_signal = sound_data_1 .* carrier;

关于一些参数：

调制指数：也叫调制深度，定义为调制信号振幅与载波振幅之间的比例。调制指数决定了调制信号对载波振幅的影响程度。

直流偏置：AM调制时需要将基带信号往上搬移的幅值，保证信号所有采样点都在正轴

3.包络检波解调

%%%%%%%%%%%%%%1.使用接口解调，包络检波%%%%%%%%%%%%%
% % 解调恢复原始信号
% demodulated_signal = amdemod(modulated_signal, carrier_freq, fs, 0, modulation_index);
% % 播放解调后的音频
%sound(demodulated_signal, fs);

%%%%%%%%%%%%%%2.希尔伯特变换的包络检波%%%%%%%%%%%%%
% demodulated_signal = abs(hilbert(modulated_signal));
% sound(demodulated_signal, fs);

%%%%%%%%%%%%%%3.接口的包络检波，等于希尔伯特%%%%%%%%%%%%%
% [upper_signal, lower_signal] = envelope(modulated_signal);
% sound(upper_signal, fs);  % fs为采样率
% subplot(2, 1, 1);
% plot(sound_data_1);
% subplot(2, 1, 2);
% plot(upper_signal);

4.相干解调

%%%%%%%%%%%%%%4.相干解调%%%%%%%%%%%%%
demodulated_signal = modulated_signal .* carrier;
% 设计低通滤波器
[b, a] = butter(6, carrier_freq/(fs/2)); % 设计6阶低通滤波器
% 低通滤波
filtered = filter(b, a, demodulated_signal); 
subplot(2, 1, 1);
plot(sound_data_1);
subplot(2, 1, 2);
plot(filtered);
sound(filtered, fs);  % fs为采样率

 5.FFT分析

%%%%%%%%%%%%%%%%%%%绘图%%%%%%%%%%%%%%%%%%
% fft点数
fft_points = length(sound_data_1);
%%%%%%%%%%%%%%画原始信号的fft%%%%%%%%%%%%%
subplot(4, 1, 1);
x1 = fs*(0:(fft_points-1))/fft_points;
y1 = abs(fft(sound_data(:, 1), fft_points));
plot(x1, y1);                             
xlabel('Frequency (Hz)');
ylabel('Magnitude');
title('FFT Spectrum');

%%%%%%%%%%%%%%画加了偏置原始信号的fft%%%%%%%%%%%%%
subplot(4, 1, 2);
x2 = fs*(0:(fft_points-1))/fft_points;
y2 = abs(fft(sound_data_1, fft_points));
plot(x2, y2);                             
xlabel('Frequency (Hz)');
ylabel('Magnitude');
title('FFT Spectrum');

%%%%%%%%%%%%%画am调制信号的fft%%%%%%%%%%%%%
subplot(4, 1, 3);
x3 = fs*(0:(fft_points-1))/fft_points;
y3 = abs(fft(modulated_signal, fft_points));
plot(x3, y3);                             
xlabel('Frequency (Hz)');
ylabel('Magnitude');
title('FFT Spectrum');

%%%%%%%%%%%%%画解调调制信号的fft%%%%%%%%%%%%%
subplot(4, 1, 4);
x4 = fs*(0:(fft_points-1))/fft_points;
y4 = abs(fft(demodulated_signal, fft_points));
plot(x4, y4);                            
xlabel('Frequency (Hz)');
ylabel('Magnitude');
title('FFT Spectrum');

6.完整代码

% AM调制

% 读取音频文件
filename = 'jay.wav';
[sound_data, fs] = audioread(filename);  % 9507502x2 44100
sound_data_1 =  sound_data(:, 1);
sound_data_1 = sound_data_1';             % 转置
% 调制参数
carrier_freq = 1000;  % 载波频率
modulation_index = 1; % 调制指数
dc = 1;               % 直流偏置

% 创建载波信号
t = (0:length(sound_data_1)-1) / fs;
carrier = cos(2*pi*carrier_freq*t);

% 进行AM调制
sound_data_1 = dc + modulation_index*sound_data_1;  %直流偏置，乘以调制指数在偏置    
modulated_signal = sound_data_1 .* carrier;



%%%%%%%%%%%%%%1.使用接口解调，包络检波%%%%%%%%%%%%%
% % 解调恢复原始信号
% demodulated_signal = amdemod(modulated_signal, carrier_freq, fs, 0, modulation_index);
% % 播放解调后的音频
%sound(demodulated_signal, fs);

%%%%%%%%%%%%%%2.希尔伯特变换的包络检波%%%%%%%%%%%%%
% demodulated_signal = abs(hilbert(modulated_signal));
% sound(demodulated_signal, fs);

%%%%%%%%%%%%%%3.接口的包络检波，等于希尔伯特%%%%%%%%%%%%%
% [upper_signal, lower_signal] = envelope(modulated_signal);
% sound(upper_signal, fs);  % fs为采样率
% subplot(2, 1, 1);
% plot(sound_data_1);
% subplot(2, 1, 2);
% plot(upper_signal);

%%%%%%%%%%%%%%4.相干解调%%%%%%%%%%%%%
demodulated_signal = modulated_signal .* carrier;
% 设计低通滤波器
[b, a] = butter(6, carrier_freq/(fs/2)); % 设计6阶低通滤波器
% 低通滤波
filtered = filter(b, a, demodulated_signal); 
subplot(2, 1, 1);
plot(sound_data_1);
subplot(2, 1, 2);
plot(filtered);
sound(filtered, fs);  % fs为采样率



% %%%%%%%%%%%%%%%%%%%绘图%%%%%%%%%%%%%%%%%%
% % fft点数
% fft_points = length(sound_data_1);
% %%%%%%%%%%%%%%画原始信号的fft%%%%%%%%%%%%%
% subplot(4, 1, 1);
% x1 = fs*(0:(fft_points-1))/fft_points;
% y1 = abs(fft(sound_data(:, 1), fft_points));
% plot(x1, y1);                             
% xlabel('Frequency (Hz)');
% ylabel('Magnitude');
% title('FFT Spectrum');
% 
% %%%%%%%%%%%%%%画加了偏置原始信号的fft%%%%%%%%%%%%%
% subplot(4, 1, 2);
% x2 = fs*(0:(fft_points-1))/fft_points;
% y2 = abs(fft(sound_data_1, fft_points));
% plot(x2, y2);                             
% xlabel('Frequency (Hz)');
% ylabel('Magnitude');
% title('FFT Spectrum');
% 
% %%%%%%%%%%%%%画am调制信号的fft%%%%%%%%%%%%%
% subplot(4, 1, 3);
% x3 = fs*(0:(fft_points-1))/fft_points;
% y3 = abs(fft(modulated_signal, fft_points));
% plot(x3, y3);                             
% xlabel('Frequency (Hz)');
% ylabel('Magnitude');
% title('FFT Spectrum');
% 
% %%%%%%%%%%%%%画解调调制信号的fft%%%%%%%%%%%%%
% subplot(4, 1, 4);
% x4 = fs*(0:(fft_points-1))/fft_points;
% y4 = abs(fft(demodulated_signal, fft_points));
% plot(x4, y4);                            
% xlabel('Frequency (Hz)');
% ylabel('Magnitude');
% title('FFT Spectrum');