delta_song.m

audio compression matlab code

%*******************************************************
% Acest program..
%*******************************************************

clc; clear;clf;

file = 'sound.wav';
file = 'speech.wav';

[ys,fs,nbits]=wavread(file);
[m,m1] = size(ys);
if (m1 == 2),           % stereo
    y1=ys(:,1); y2=ys(:,2);
    ym=(y1+y2)/2;
else 
    ym = ys;
end;

N=length(ym);
ts=1/fs;
t=0:ts:(N-1)*ts;
%subplot(211), plot(t,y1,t,y2,'r'); subplot(212), stairs(t,y1); hold on; stairs(t,y2,'r');
%wavplay(y1); pause; wavplay(y2);
%wavplay(yt);


% defineste vectorii scurti:
n = N;
x = ym(1:n);     % intrarea;
t = t(1:n);

q0 = 0.001;	       % valoarea minima a cuantei;
q = q0;
y=zeros(n,1);      % vectorul de iesire, aproximat/refacut local; 

b_new = -1;      % valoarea bitului nou;
b_old = -1;      % valoarea bitului vechi;

% modulatie uniforma
b=[-1];
for k = 2:n,
  if  x(k) > y(k-1),  b_new = 1; else b_new = -1; end;
  b = [b b_new];
  % reconstructie:
  if b_new == b_old, q = q + q0; else q = q - q0; end;
  y(k) = y(k-1) + q * b_new; 
  b_old = b_new;
end;

[dt,dy]=stairs(t,y);
[dt,dx]=stairs(t,x);
subplot(211), plot(dt,dx,'b',dt,dy,'r-');
subplot(212), stairs(b(n-50:n));
file_input_size = n * nbits / 8 ; % mono channal;
file_output_size = n / 8 ; % mono channal;
compression_ratio = file_input_size / file_output_size

% semnalul refacut dupa compresie:
wavwrite(y,fs,nbits,'compressed_song.wav');