CIC抽取----代码：
r = 2;                  % Decimation factor.
hm = mfilt.cicdecim(r); % Use default NumberOfSections &
                        % DifferentialDelay property values.
fs = 44.1e3;            % Original sampling frequency: 44.1kHz.
n = 0:10239;            % 10240 samples, 0.232 second long signal.
x  = sin(2*pi*1e3/fs*n);% Original signal, sinusoid at 1kHz.

y_fi = filter(hm,x); % 5120 samples, still 0.232 seconds.
  
% Scale the output to overlay the stem plots.
x = double(x);
y = double(y_fi);
y = y/max(abs(y));
stem(n(1:44)/fs,x(2:45)); hold on;  % Plot original signal  
                                      % sampled at 44.1kHz.
stem(n(1:22)/(fs/r),y(3:24),'r','filled'); % Plot decimated
                                           % signal (22.05kHz)
                                           % in red.
xlabel('Time (seconds)');ylabel('Signal Value');