%Program 11.1 Audio codec
n=32;                                 % length of window
nb=127;                               % number of windows; must be > 1
b=16; L=1;                             % quantization information
q=2*L/(2^b-1);                        % b bits on interval [-L, L]
for i=1:n                             % form the MDCT matrix
  for j=1:2*n
    M(i,j)= cos((i-1+1/2)*(j-1+1/2+n/2)*pi/n);
  end
end
M=sqrt(2/n)*M;
N=M';                                 % inverse MDCT
Fs=8192;f=8;                          % Fs=sampling rate, f is multiple of base freq.
x=cos((1:4096)*pi*64*f/4096);         % test signal
sound(x,Fs)                           % Matlab's sound command
out=[];
h = sqrt(2)*sin(((1:2*n)-.5)*pi/(2*n)); % Window Function
for k=1:nb                            % loop over windows
  x0=x(1+(k-1)*n:2*n+(k-1)*n)';
  x0 = x0.*h';                      % Apply Window Function
  y0=M*x0;
  y1=round(y0/q);                     % transform components quantized
  y2=y1*q;                            %                and dequantized
  w(:,k)=N*y2;                        % invert the MDCT
  if(k>1)
      w2=w(n+1:2*n,k-1);w3=w(1:n,k);
      w2=w2.*h(n+1:2*n)';           % Window Function Application
      w3=w3.*h(1:n)';               % Window Function Application
      out=[out;(w2+w3)/2];            % collect the reconstructed signal
  end
end
pause(1)
sound(out,Fs)

Published with MATLAB® R2013a