f_nonlin_compand.m

audio compression matlab code

function y = f_nonlin_compand(x, type, V, nbits_in, nbits_out)

% nonlinear transforms compander
% type == 1,    % compression;
% else  extension
% V is the maximum value of output and input

n = length(x);

if type == 1,    % compression;
    % define the range
    x_min = - 2^nbits_in  ;
    x_max = + 2^nbits_in -1;
    in_range =  x_max - x_min;
    y_min = - 2^nbits_out  ;
    y_max = + 2^nbits_out -1;
    out_range =  y_max - y_min;

    if nbits_in < nbits_out,  disp('error 1'); end;
    for i=1:n,
    	if x(i) >= 0,
            y(i) = out_range * log2(x(i) /  in_range + 1) / 2;
    	else
            y(i) = -out_range * log2(x(i) / in_range - 1) / 2;
    	end;
    end;
    y = y./(max(abs(y)));
    y = y .* V;

else % extension
    % define the range
    x_min = - 2^nbits_in  ;
    x_max = + 2^nbits_in -1;
    in_range =  x_max - x_min;
    y_min = - 2^nbits_out  ;
    y_max = + 2^nbits_out -1;
    out_range =  y_max - y_min;

    if nbits_in > nbits_out,  disp('error 2'); end;
    for i=1:n,
        if x(i) >=0,
            xb(i) = in_range * 2^(2*x(i) / out_range) - in_range;
        else
            xb(i) = - in_range *( -1 / ( 2^(2*x(i) / out_range)) )  + in_range ;
        end;
    end;
    xb = xb./(max(abs(xb)));
    xb = xb .* V;
    y = xb;
end;