aspec(B,A,Fs);

function aspec(B,A,Fs); 
% ASPEC  Plots a filter characteristics vs. A-weighting specifications. 
%    ASPEC(B,A,Fs) plots the attenuation of the filter defined by B and A 
%    with sampling frequency Fs against the specifications for class 1 
%    and class 2 A-weighting filters. 
%
%    See also ADSGN, CDSGN, CSPEC. 

% Author: Christophe Couvreur, Faculte Polytechnique de Mons (Belgium)
%         [e-mail]
% Last modification: Aug. 26, 1997, 10:00am.

% References: 
%    [1] IEC/CD 1672: Electroacoustics-Sound Level Meters, Nov. 1996. 


if (nargin ~= 3) 
  error('Invalide number of arguments.');
end

N = 512; 
W = 2*pi*logspace(log10(10),log10(Fs/2),N);
H = freqz(B,A,W/Fs);
fref = [10, 12.5 16 20, 25 31.5 40, 50 63 80, 100 125 160, 200 250 315, ...
    400 500 630, 800 1000 1250, 1600 2000 2500, 3150 4000 5000, ...
	6300 8000 10000, 12500 16000 20000 ];
Agoal = [-70.4, -63.4 -56.7 -50.5, -44.7 -39.4 -34.6, -30.2 -26.2 -22.5, ...
	-19.1 -16.1 -13.4, -10.9 -8.6 -6.6, -4.8 -3.2 -1.9, -.8 0 .6, ...
	1 1.2 1.3, 1.2, 1 .5, -.1 -1.1 -2.5, -4.3 -6.6 -9.3 ];
up1 = [ 3, .25 2 2, 2 1.5 1, 1 1 1, 1 1 1, 1 1 1, 1 1 1, 1 0.7 1, ...
	1 1 1, 1 1 1.5, 1.5 1.5 2, 2 2.5 3 ];
low1 = [ inf, inf 4 2, 1.5 1.5 1, 1 1 1, 1 1 1, 1 1 1, 1 1 1, 1 0.7 1, ...
	1 1 1, 1 1 1.5, 2 2.5 3, 5 8 inf ];
up2 = [ 5, 5 5 3, 3 3 2, 2 2 2, 1.5 1.5 1.5, 1.5 1.5 1.5, 1.5 1.5 1.5, ...
	1.5 1 1.5, 2 2 2.5, 2.5 3 3.5, 4.5 5 5, 5 5 5 ];
low2 = [ inf, inf inf 3, 3 3 2, 2 2 2, 1.5 1.5 1.5, 1.5 1.5 1.5, ...
    1.5 1.5 1.5, 1.5 1 1.5, 2,2 2.5, 2.5 3 3.5, 4.5 5 inf, inf inf inf ];
clf;
semilogx(W/2/pi,20*log10(abs(H)),'-',fref,Agoal+up1,'--',fref,Agoal+up2,':'); 
hold on 
semilogx(W/2/pi,20*log10(abs(H)),'-',fref,Agoal-low1,'--',fref,Agoal-low2,':'); 
hold off
xlabel('Frequency [Hz]'); ylabel('Gain [dB]');
title(['A-weighting, Fs = ',int2str(Fs),' Hz']);
axis([fref(1)  max(fref(34),Fs/2) -75 5]);
legend('Filter','Class 1','Class 2',0);