dfirauop.m

ADSP TOOLBOX: Version 2.0 and gui m-files

function nr = dfirauop(ty,a,sf,fp,fs)
% FIRAUOPT for auto optimal-design
%       N = auto_opt(TY,A,SF,FP,FS) Remez Parks-McCllelan optimal filter
%	TY can be 'lp', 'hp', 'bp', or 'bs',
%       If A = [Ap As], Ap As are the passband and stopband attenuation in dB
%       SF is the sampling frequency in HERTZ
%	FP and FS are the passband & stopband edge(s) in HERTZ
%       NOTE 1:  No windows are used in optimal design
%	N returns length

% Author: Ashok Ambardar <[e-mail]>
% Date: 2/2/96 11:32AM
% Copyright (c) 1997 by Prentice-Hall, Inc.

%COMPUTE RIPPLE & PREPARE FOR REMEZ
ap=a(1);
as=a(2);
%dp=[(10)^(0.05*ap)-1]/[(10)^(0.05*ap)+1];
dp=[1-(10)^(-0.05*ap)]/2;  % For measures from 0 dB
ds=(10)^(-0.05*as);
delt=1-dp;
dp=dp/delt;
ds=ds/delt;
k=ds/dp;
fp=fp/sf;
fs=fs/sf;
odd=0;

%%%%%%  NEW:   MAKE FREQUENCIES SYMMETRIC  %%%%%%%%%%%%%%%%%%%%%%%%
if ty < 3,
fpp=fp;
fss=fs;
df=abs(fs-fp);
else,
df1=abs(fp(1)-fs(1));
df2=abs(fs(2)-fp(2));
df=min(df1,df2);
fpp=0.5*abs(diff(fp));
fss=fpp+df;
if ty == 3
fs=[fp(1)-df fp(2)+df];  % New stopband
else
fs=[fp(1)+df fp(2)-df];  % New stopband
end
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


if ty==1,
   M=[1 1 0 0];
   F=2*[0 fp fs 0.5];
   W=[k 1];
 elseif ty==2,
   odd=1;
   M=[0 0 1 1];
   F=2*[0 fs fp 0.5];
   W=[1 k];
 elseif ty==3,
   M=[0 0 1 1 0 0];
   F=2*[0 fs(1) fp(1) fp(2) fs(2) 0.5];
   W=[1 k 1];
 else,
   odd=1;
   M=[1 1 0 0 1 1];
   F=2*[0 fp(1) fs(1) fs(2) fp(2) 0.5];
   W=[k 1 k];
 end



%DETERMINE FILTER LENGTH N
if exist('remlpord')>0, %For compatibility with v3.5 etc
N=ceil(eval('remlpord(fpp,fss,dp,ds)'));
else
N=ceil(1-(10*log10(dp*ds)+13)/(2.324*2*pi*df));
end


if rem(N,2)==1,
   if odd==1,
      N=N-1;
   end;
end,

N=max(2,N);
j=sqrt(-1);
f=0:1/400:0.5;
z=exp(j*2*pi*f);

%REMEZ LOOP
k=0;iter=0;
rs=2*ds;
rp=2*dp;
while rs>ds | rp>dp
   k=k+1;iter=iter+1;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   if iter>15,break,end  % Precaution measure
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   if odd==1,
      N=N+2;
   else,
      N=N+1;
   end
h=remez(N,F,M,W);
mag=abs(polyval(h,z));

rp=max(mag)-1;

if ty==1,
   i=find(f>fs);
elseif ty==2,
   i=find(f<fs);
elseif ty==3,
   i=find(f<fs(1) | f>fs(2));
else,
   i=find(f>fs(1) & f<fs(2));
end
rs=mag(i);
rs=max(rs);
if k==1,
   if rs<=ds & rp<=dp,
      rs=2*ds;
      rp=2*dp;
      k=0;
    if N<5
     break
    else
      if odd==1,
         N=N-4;
      else,
         N=N-3;
      end;
   end,
end
end

end
nr=N+1;