test_2.m

audio compression matlab code

clc; clear; clf;
% nonlinear transforms 

%the numbar of the inputs bits...
% only pozitive values ...
nbits_in = 15 ; 
nbits_out = 7;

% define the range
x_min = -2^nbits_in  ;
x_max = + 2^nbits_in -1;
in_range =  x_max - x_min;

step = 100;
x = x_min:step:x_max;

y_min = - 2^nbits_out  ;
y_max = + 2^nbits_out -1;
out_range =  y_max - y_min;

n=length(x);
for i=1:n,
    xx = out_range * log2(x(i) / in_range + 1) / 2;
    if x(i) >=0,
        y(i) = xx; else y(i) = + xx; 
    end;
end;

xb = (in_range / out_range) * y;
subplot(221), stairs(x,y); title('Compression'); 
subplot(222), stairs(y,xb,'r'); title('Expanding')


% transfer characteristic ...
% x = -max(I_all) : 0.01: max(I_all);
% xc = f_bit_compression(x, nbits_in, nbits_out);
subplot(223), stairs(x,xb);

subplot(224),stairs(x, (xb -x) ./ x .* 100); 
title('Reconstruction Error [%]');