postfilt.m

the implement of the encoder and the decoder of the CELP

function [ s, powerin, powerout, dp1, dp2, dp3 ] = ...
         postfilt( s, l, alpha, beta, powerin, powerout, dp1, dp2, ...
                   dp3, lpc_coef, no )

global TC ipZ opZ

ast = zeros( 1, 2 );      % Initialize local filter memory

% Estimate input power
[ newpowerin, ipZ ] = filter( [TC 0], [1 -1+TC], ( s .* s ), ipZ );
powerin = newpowerin(l);

pcexp1 = wcoff( beta, lpc_coef );               % Do bandwinth expansion on predictor poles
pcexp2 = wcoff( alpha, lpc_coef );


[ s, dp1 ] = FIRfilter( pcexp1, dp1, s );        % Apply pole-zero postfilter
[ s, dp2 ] = lpcr( pcexp2, dp2, s );


rcexp2 = poly2rc( pcexp2 );                      % Convert LPC to RC (MATLAB high level command)
rcexp2 = -rcexp2';


% Add tilt compensation
ast(1) = 1.0;
if rcexp2(1) > 0.0
    ast(2) = -0.5 * rcexp2(1);
else
    ast(2) = 0.00;
end
[ s, dp3 ] = FIRfilter( ast, dp3, s, 1);

% Estimate output power
[ newpowerout, opZ ] = filter( [TC 0], [1 -1+TC], ( s .* s ), opZ );
powerout = newpowerout(l);

% Incorporate automatic gain control
agcUnity = find( newpowerout <= 0 );
newpowerout( agcUnity ) = ones( length( agcUnity ), 1 );
agcScale = sqrt( newpowerin ./ newpowerout );
agcScale( agcUnity ) = ones( length( agcUnity ), 1 );
s = s .* agcScale;