数字信号处理（MATLAB入门例子）

（代码主要来源于这本书）

1.用MATLAB产生32个正弦波样本，A=2，f=1000Hz，以及fs=8000Hz

%
% Example 2.1 Sinewave generator
% This example generate 32 sine sample,
% plot it and save in sine.dat file
 
% For the book "Real Time Digital Signal Processing: 
%               Fundamentals, Implementation and Application, 3rd Ed"
%               By Sen M. Kuo, Bob H. Lee, and Wenshun Tian
%               Publisher: John Wiley and Sons, Ltd
 
n = [0:31];             % Time index n
omega = 0.25*pi;        % Digital frequency
xn = 2*sin(omega*n);    % Sinewave generation
plot(n, xn, '-o');      % Samples are marked by 'o'
xlabel('Time index, n'); 
ylabel('Amplitude');
axis([0 31 -2 2]);		% Define ranges of plot
save sine.dat xn -ascii;% Save in ASCII data file

例2：绘制传递函数的零极点图：

% Example 2.11a Mgnitude and phase response of an IIR filter
% This example plots magnitude and phase response of an IIR filter
 
% For the book "Real Time Digital Signal Processing: 
%               Fundamentals, Implementation and Application, 3rd Ed"
%               By Sen M. Kuo, Bob H. Lee, and Wenshun Tian
%               Publisher: John Wiley and Sons, Ltd
 
b=[1];          % Define numerator
a=[1, -1, 0.9]; % Denominator 
zplane(b,a);    % Pole-zero plot

例3：正弦波A=1,f=1000Hz,采样率为 10 000Hz,可以产生100个正弦波采样样本。信号的幅度谱可以采用以下MATLAB程序绘制：

% example2_16.m - Compute and plot amplitude spectrum of sinewave
%
 
% For the book "Real Time Digital Signal Processing: 
%               Fundamentals, Implementation and Application, 3rd Ed"
%               By Sen M. Kuo, Bob H. Lee, and Wenshun Tian
%               Publisher: John Wiley and Sons, Ltd
 
N=100; f = 1000; fs = 10000; % Define parameter values
n=[0:N-1]; k=[0:N-1];        % Define time and frequency indices
omega=2*pi*f/fs;             % Frequency of sinewave
xn=sin(omega*n);             % Generate sinewave
Xk=fft(xn,N);                % Perform DFT
magXk=20*log10(abs(Xk));     % Compute magnitude spectrum
plot(k, magXk); axis([0, N/2, -inf, inf]); % plot from 0 to pi
xlabel('Frequency index, k');
ylabel('Magnitude (dB)');

例4：绘制下面这个传递函数的幅度响应和相位响应

% For the book "Real Time Digital Signal Processing: 
%               Fundamentals,Implementation and Application, 3rd Ed"
%               By Sen M. Kuo, Bob H. Lee, and Wenshun Tian
%               Publisher: John Wiley and Sons, Ltd
 
b=[1, 0, 0, 0, 0, 0, 0, 0, -1]; % Numerator
a=[1, -1];                      % Denominator
freqz(b,a);                     % Plot frequency response

例5：本例产生中的一个包含噪声的正弦波信号，其中噪声是零均值、单位方差白噪声所示。

 
N=256; A=sqrt(2); w0=0.2*pi;   % Define parameters
n = [0:N-1];                   % Time index
sn = A*sin(w0*n);              % Sine sequence
sd = 12357;                    % Define seed value
rng(sd);                       % Use defined seed
vn = (rand(1,N)-0.5)*sqrt(12); % Zero-mean, unit-variance white noise
xn = sn+vn;     % Sinewave embedded in white noise
plot(n,xn);
save xn.dat xn -ascii ;