f_firwin.m

DSP程序 Matlab是一套用于科学工程计算的可视化高性能语言与软件环境。它集数值分析、矩阵运算、信号处理和图形显示于一体

function b = f_firwin (fun,m,fs,win,sym,p)

%F_FIRWIN: Design a general windowed FIR filter
%
% Usage: b = f_firwin (fun,m,fs,win,sym,p)
%
% Inputs: 
%         fun = string containing name of function which 
%               specifies the desired amplitude response 
%               of the filter. Usage:
%
%               A = fun(f,fs,p)
%
%               Here f is the frequency, fs is the sampling 
%               frequency, and p is an option parameter 
%               vector containing things like cutoff 
%               frequencies,etc. The output A is a the 
%               desired amplitude response.
%
%         m   = the filter order
%         fs  = sampling frequency
%         win = the window type to be used:
%
%               0 = rectangular
%               1 = Hanning
%               2 = Hamming
%               3 = Blackman
% 
%         sym = symmetry of pulse response.  
%
%               0 = even symmetry of h(k) about k = m/2
%               1 = odd symmetry of h(k) about k = m/2
%
%         p   = an optional vector of length contained 
%               design paramaters to be passed to fun.  
%               For example p might contain cutoff 
%               frequencies or gains.
% Outputs: 
%          b = 1 by m+1 vector of filter coeficients. The 
%              filter output is
%
%              y(k) = b[1]*x[k] + b[2]*x[k-1] + ... 
%                     + b[m+1]*x[k-m]  
% Notes:    
%        1. To design a frequency-selective filter, you 
%           can use f_firamp for the calling argument fun, 
%           or you can use f_firideal in place of f_firwin.
%
%        2. The linear-phase filter type is determined by
%           combination of sym and n:
%   
%           sym    m      type
%            0    even     1
%            0    odd      2
%            1    even     3
%            1    odd      4
%
% See also: F_FIRAMP, F_FIRIDEAL, F_FIRSAMP, F_FIRLS, 
%           F_FIRPARKS, F_FREQZ    

% Initialize

m = f_clip(m,0,m);
m2 = floor(m/2);
win = f_clip(win,0,3);
b = zeros (1,m+1);
M = 100;
fn = fs/2;
T = 1/fs;
df = fn/M;
pp = nargin - 5;

% Compute filter coefficients using Simpson's rule
% NOTE: Maybe call quadL with local function instead?

wstr = sprintf ('Computing %d FIR filter coefficients...',m+1);   
w = waitbar (0,wstr);   
for k = 0 : m
   waitbar (k/m,w);
   if sym == 0
      if pp
         b(k+1) = feval(fun,0,fs,p) + cos(2*pi*(k-0.5*m)*fn*T)*feval(fun,fn,fs,p);
      else
         b(k+1) = feval(fun,0,fs) + cos(2*pi*(k-0.5*m)*fn*T)*feval(fun,fn,fs);
      end         
      for i = 1 : M-1
         f = i*df;
         if pp
            if mod(i,2)
               b(k+1) = b(k+1) + 4*cos(2*pi*(k-0.5*m)*f*T)*feval(fun,f,fs,p);
            else
               b(k+1) = b(k+1) + 2*cos(2*pi*(k-0.5*m)*f*T)*feval(fun,f,fs,p); 
            end
         else
            if mod(i,2)
               b(k+1) = b(k+1) + 4*cos(2*pi*(k-0.5*m)*f*T)*feval(fun,f,fs);
            else
               b(k+1) = b(k+1) + 2*cos(2*pi*(k-0.5*m)*f*T)*feval(fun,f,fs); 
            end
         end
      end  
      b(k+1) = 2*T*df*b(k+1)/3;
   else
      if pp
         b(k+1) = feval(fun,0,fs,p) - sin(2*pi*(k-0.5*m)*fn*T)*feval(fun,fn,fs,p);
      else
         b(k+1) = feval(fun,0,fs) - sin(2*pi*(k-0.5*m)*fn*T)*feval(fun,fn,fs);
      end
      for i = 1 : M-1
         f = i*df;
         if pp
            if mod(i,2)
               b(k+1) = b(k+1) - 4*sin(2*pi*(k-0.5*m)*f*T)*feval(fun,f,fs,p);
            else
               b(k+1) = b(k+1) - 2*sin(2*pi*(k-0.5*m)*f*T)*feval(fun,f,fs,p); 
            end
         else
            if mod(i,2)
               b(k+1) = b(k+1) - 4*sin(2*pi*(k-0.5*m)*f*T)*feval(fun,f,fs);
            else
               b(k+1) = b(k+1) - 2*sin(2*pi*(k-0.5*m)*f*T)*feval(fun,f,fs); 
            end
         end
      end  
      b(k+1) = 2*T*df*b(k+1)/3;
   end
end
close (w);

% Add window

w = f_window (win,m);
b = b .* w;
b = real(b);