function [g,f] = octspec(B,A,Fs,Fc,s,n); % OCTSPEC Plots an octave filter characteristics.%    OCTSPEC(B,A,Fs,Fc) plots the attenuation of the filter defined by%    B and A at sampling frequency Fs. Fc is the center frequency of%    the octave filter. The plot covers one decade on both sides of Fc.%%    OCTSPEC(B,A,Fs,Fc,'ANSI',N) superposes the ANSI Order-N analog%    specification for comparison. Default is N = 3.%%    OCTSPEC(B,A,Fs,Fc,'IEC',N) superposes the characteristics of the%    IEC 61260 class N specification for comparison. Default is N = 1. %%    [G,F] = OCTSPEC(B,A,Fs,Fc) returns two 512-point vectors with%    the gain (in dB) in G and logarithmically spaced frequencies in F.%    The plot can then be obtained by SEMILOGX(F,G)% 					%    See also OCTDSGN, OCT3SPEC, OCT3DSGN.% Author: Christophe Couvreur, Faculte Polytechnique de Mons (Belgium)%         couvreur@thor.fpms.ac.be% Last modification: Sept. 4, 1997, 10:30am.% References:%    [1] ANSI S1.1-1986 (ASA 65-1986): Specifications for%        Octave-Band and Fractional-Octave-Band Analog and%        Digital Filters, 1993.%    [2] IEC 61260 (1995-08):  Electroacoustics -- Octave-Band and%        Fractional-Octave-Band Filters, 1995.   if (nargin < 4) | (nargin > 6)   error('Invalid number of input arguments.');endansi = 0;iec = 0;if nargin > 4  if strcmp(lower(s),'ansi')    ansi = 1;    if nargin == 5      n = 3;    end  elseif strcmp(lower(s),'cei') | strcmp(lower(s),'iec')    iec = 1;    if nargin == 5      n = 1    end    if (n < 0) | (n > 3)       error('IEC class must be 0, 1, or 2');    end  endendN = 512;pi = 3.14159265358979;F = logspace(log10(Fc/10),log10(min(Fc*10,Fs/2)),N);H = freqz(B,A,2*pi*F/Fs);G = 20*log10(abs(H));% Set output variables. if nargout ~= 0  g = G; f = F;   returnend% Generate the plotif (ansi) 				% ANSI Order-n specification  f = logspace(log10(Fc/10),log10(Fc*10),N);  f1 = Fc/sqrt(2);  f2 = Fc*sqrt(2);  Qr = Fc/(f2-f1);  Qd = (pi/2/n)/(sin(pi/2/n))*Qr;  Af = 10*log10(1+Qd^(2*n)*((f/Fc)-(Fc./f)).^(2*n));  semilogx(F,G,f,-Af,'--');  legend('Filter',['ANSI order-' int2str(n)],0); elseif (iec) 					% CEI specification  semilogx(F,G);  hold on  if n == 0     tolup =  [ .15 .15 .15 .15 .15 -2.3 -18.0 -42.5 -62 -75 -75 ];    tollow = [ -.15 -.2 -.4 -1.1 -4.5 -realmax -inf -inf -inf -inf -inf ];  elseif n == 1    tolup =  [ .3 .3 .3 .3 .3 -2 -17.5 -42 -61 -70 -70 ];    tollow = [ -.3 -.4 -.6 -1.3 -5 -realmax -inf -inf -inf -inf -inf ];  elseif n == 2    tolup =  [ .5 .5 .5 .5 .5 -1.6 -16.5 -41 -55 -60 -60  ];    tollow = [ -.5 -.6 -.8 -1.6 -5.5 -realmax -inf -inf -inf -inf -inf ];  end  U = 2;   f = Fc * U.^[ 0 1/8 1/4 3/8 1/2 1/2 1 2 3 4 NaN ];     ff = Fc * U.^[ 0 -1/8 -1/4 -3/8 -1/2 -1/2 -1 -2 -3 -4 NaN ];     f(length(f)) = realmax;   ff(length(ff)) = realmin;    semilogx(F,G,f,tolup,'--');  semilogx(F,G,f,tollow,'--');  semilogx(F,G,ff,tolup,'--');  semilogx(F,G,ff,tollow,'--');  hold off  legend('Filter',['IEC class ' int2str(n)],0); else  semilogx(F,G);endxlabel('Frequency [Hz]'); ylabel('Gain [dB]');title(['Octave filter: Fc =',int2str(Fc),' Hz, Fs = ',int2str(Fs),' Hz']);axis([Fc/10 Fc*10 -80 5]);grid on