f_firamp.asv

digital signal processing常用工具箱

function A = f_firamp (f,fs,p);

%F_FIRAMP: Compute amplitude response of frequency-selective filter

% Usage:       A = f_firamp (f,fs,p);
%
% Description: Return the amplitude response of filter at 
%              frequency f using sampling frequency fs and
%              parametrs p.
%
% Entry:       f  = vector of length N contain input frequencies
%              fs = sampling frequency
%              p  = vector containing filter parameters
%
%                   p(1) = filter type
%
%                          0 = lowpass
%                          1 = highpass
%                          2 = bandpass
%                          3 = bandstop
%
%                   p(2) = first cutoff frequency, F_0
%                   p(3) = second cutoff frequency, F_1
%                   p(4) = transition bandwidth, B
%            
% Exit:        A  = vector containing amplitude response evaluated 
%                   at vector f.
% Note: This is used by f_firwin     
%
% See also;    f_firwin
%-------------------------------------------------------------------

% Initialize

A = zeros(size(f));
f_type = p(1);
F_0 = p(2);
F_1 = p(3);
B = p(4);

% Compute amplitude

switch (f_type)
   
case 0,
   
   i1 = find(f <= F_0);
   A(i1) = 1;
   i2 = find((f > F_0) & (f < F_0+B));
   A(i2) = 1 - (f(i2)-F_0)/B; 
   
case 1,
   
   i1 = find(f >= F_1);
   A(i1) = 1;
   i2 = find((f > F_1-B) & (f < F_1));
   A(i2) = (f(i2) - (F_1-B))/B;
   
case 2,
   
   i1 = find((f >= F_0) & (f <= F_1));
   A(i1) = 1;
   i2 = find((f > F_0-B) & (f < F_0));
   A(i2) = (f(i2) - (F_0-B))/B;
   i3 = find((f > F_1) & (f < F_1+B));
   A(i3) = 1 - (f(i3)-F_1)/B;
   
case 3,
   
   i1 = find((f <= F_0-B) | (f >= F_1+B));
   A(i1) = 1;
   i2 = find((f > F_0-B) & (f < F_0));
   A(i2) = 1 - (f(i2) - (F_0-B))/B;
   i3 = find((f > F_1) & (f < F_1+B));
   A(i3) = (f(i3)-F_1)/B;
   
end

%-------------------------------------------------------------------