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 = 10e3; % 载波频率
modulation_index = 1; % 调制指数
dc = 0; % 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;
% modulated_signal = awgn(modulated_signal, 10, 'measured'); % 添加高斯白噪声
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。
3.相干解调
DSB只能使用相干解调
%%%%%%%%%%%%%相干解调%%%%%%%%%%%%% % demodulated_signal = modulated_signal .* carrier; % 理想情况下的相干解调，同频同相 carrier_new = cos(2*pi*carrier_freq*t+pi/4); % 一般情况下的相干解调，有个相位偏移 demodulated_signal = modulated_signal .* carrier_new; % 设计低通滤波器 [b, a] = butter(20, 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
4.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');
5.完整代码
% DSB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 = 10e3; % 载波频率 modulation_index = 1; % 调制指数 dc = 0; % 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; modulated_signal = awgn(modulated_signal, 40, 'measured'); % 添加高斯白噪声 %%%%%%%%%%%%%相干解调%%%%%%%%%%%%% % demodulated_signal = modulated_signal .* carrier; % 理想情况下的相干解调，同频同相 carrier_new = cos(2*pi*carrier_freq*t+pi/4); % 一般情况下的相干解调，有个相位偏移 demodulated_signal = modulated_signal .* carrier_new; % 设计低通滤波器 [b, a] = butter(20, 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
6.说明
①、频谱分析
假设调制指数为1，则DSB调制信号在Fc处左右各有一个带宽的基带信号，总共占用带宽为2B【B为基带信号的带宽】
