f_firparks.asv

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function [b,n] = f_firparks (m,F_p,F_s,delta_p,delta_s,ftype,fs)

% F_FIRPARKS: Design a linear-phase Parks-McClellan equiripple FIR filter
%
% Usage: b = f_firparks (m,F_p,F_s,delta_p,delta_s,ftype,fs)
%
% Inputs: m       = filter order (m >= 2)
%         F_p     = passband cutoff frequency or frequencies
%         F_s     = stopband cutoff frequency or frequencies
%         delta_p = passband ripple
%         delta_s = stopband attenuation
%         ftype   = filter type
%
%                   0 = lowpass
%                   1 = highpass
%                   2 = bandpass (F_p and F_s are vectors)
%                   3 = bandstop (F_p and F_s are vectors)
%
%         fs      = sampling frequency in Hz
%
% Outputs: b = 1 by (m+1) coefficient vector of numerator polynomial 
%          n = optional estimate of filter order needed to meet specs.
%
% Note: This function uses the MATLAB Signal Processing toolbox, if 
%       it is available.  Otherwise, it uses a local implementation
%       of the equirippled FIR filter design procedure based on a
%       free C version deleloped by Jake Janovetz ([e-mail]).
%
% See also: F_FIRWIN, F_FIRIDEAL, F_FIRSAMP, F_FIRLS, F_FREQZ

% Initialize

m = f_clip (m,2,m);
if mod(m,2)
    m = m + 1;
end
p = m/2;
fs = f_clip (fs,0,fs);
F_p = f_clip (F_p,0,fs/2);
F_s = f_clip (F_s,0,fs/2);
delta_p = f_clip (delta_p,0,delta_p);
delta_s = f_clip (delta_s,0,delta_s);
T = 1/fs;
w = delta_s/delta_p;

% Compute estimate of required filter order

B = abs(F_p(1)-F_s(1))/fs;
n = ceil(-(10*log10(delta_p*delta_s)+13)/(14.6*B) + 1);

% Check for signal processing toolbox

if exist('remez')
    sig_proc_toolbox = 1;
else
    sig_proc_toolbox = 0;
end

if sig_proc_toolbox 

% Compute F, A, and W like in remez.dll

   switch ftype
       case 0,                                            % low pass
           F_0 = [0 F_p F_s fs/2]/(fs/2);
           A_0 = [1 1 0 0];
           W_0 = [w 1];
       case 1,                                           % high pass
           F_0 = [0 F_s F_p fs/2]/(fs/2);
           A_0 = [0 0 1 1];
           W_0 = [1 w];
       case 2,                                           %  bandpass
           F_0 = [0 F_s(1) F_p(1) F_p(2) F_s(2) fs/2]/(fs/2);
           A_0 = [0 0 1 1 0 0];
           W_0 = [1 w 1];
       case 3,                                           % bandstop
           F_0 = [0 F_p(1) F_s(1) F_s(2) F_p(2) fs/2]/(fs/2);
           A_0 = [1 1 0 0 1 1];
           W_0 = [w 1 w];
   end

% Compute equiripple filter (uses Signal Processing toolbox)

   b = remez (m,F_0,A_0,W_0);

else

% Compute F, A, and W like in parks0.dll

   switch ftype
       case 0,                                               % low pass
           F_0 = [0 F_p F_s fs/2]/fs;
           A_0 = [1 0];
           W_0 = [w 1];
           numband = 2;
       case 1,                                               % high pass
           F_0 = [0 F_s F_p fs/2]/fs;
           A_0 = [0 1];
           W_0 = [1 w];
           numband = 2;
       case 2,                                               %  bandpass
           F_0 = [0 F_s(1) F_p(1) F_p(2) F_s(2) fs/2]/fs;
           A_0 = [0 1 0];
           W_0 = [1 w 1];
           numband = 3;
       case 3,                                               % bandstop
           F_0 = [0 F_p(1) F_s(1) F_s(2) F_p(2) fs/2]/fs;
           A_0 = [1 0 1];
           W_0 = [w 1 w];
           numband = 3;
   end

% Compute equiripple filter (uses local dll file)

   type = 1;
   fprintf ('Calling f_parks.dll')
   b = f_parks (m+1,numband,F_0,A_0,W_0,type);
    
end