Các function phương pháp tần số lấy mẫu (MATLAB CODE)

Linear-phase FIR filter: đáp ứng xung đối xứng với M lẻ.

function [Hr,w,a,L] = Hr_Type1(h);
% Computes Amplitude response Hr(w) of a Type-1 LP FIR filter
% -----------------------------------------------------------
% [Hr,w,a,L] = Hr_Type1(h)
% Hr = Amplitude Response
% w = 500 frequencies between [0 pi] over which Hr is computed
% a = Type-1 LP filter coefficients
% L = Order of Hr
% h = Type-1 LP filter impulse response
%
M = length(h);
L = (M-1)/2;
a = [h(L+1) 2*h(L:-1:1)]; % 1x(L+1) row vector
n = [0:1:L]; % (L+1)x1 column vector
w = [0:1:500]'*pi/500;
Hr = cos(w*n)*a';

 Linear-phase FIR filter: Đáp ứng xung đối xứng với M chẵn.

function [Hr,w,b,L] = Hr_Type2(h);
% Computes Amplitude response of Type-2 LP FIR filter
% ---------------------------------------------------
% [Hr,w,b,L] = Hr_Type2(h)
% Hr = Amplitude Response
% w = frequencies between [0 pi] over which Hr is computed
% b = Type-2 LP filter coefficients
% L = Order of Hr
% h = Type-2 LP impulse response
%
M = length(h);
L = M/2;
b = 2*[h(L:-1:1)];
n = [1:1:L]; n = n-0.5;
w = [0:1:500]'*pi/500;
Hr = cos(w*n)*b';

 Linear-phase FIR filter: Đáp ứng xung phản đối xứng với M lẻ

function [Hr,w,c,L] = Hr_Type3(h);
% Computes Amplitude response Hr(w) of a Type-3 LP FIR filter
% -----------------------------------------------------------
% [Hr,w,c,L] = Hr_Type3(h)
% Hr = Amplitude Response
% w = frequencies between [0 pi] over which Hr is computed
% c = Type-3 LP filter coefficients
% L = Order of Hr
% h = Type-3 LP impulse response
%
M = length(h);
L = (M-1)/2;
c = [2*h(L+1:-1:1)];
n = [0:1:L];
w = [0:1:500]'*pi/500;
Hr = sin(w*n)*c';

 Linear-phase FIR filter: Đáp ứng xung phản đối xứng với M chẵn.

function [Hr,w,d,L] = Hr_Type4(h);
% Computes Amplitude response of Type-4 LP FIR filter
% ---------------------------------------------------
% [Hr,w,d,L] = Hr_Type4(h)
% Hr = Amplitude Response
% w = frequencies between [0 pi] over which Hr is computed
% d = Type-4 LP filter coefficients
% L = Order of d
% h = Type-4 LP impulse response
%
M = length(h);
L = M/2;
d = 2*[h(L:-1:1)];
n = [1:1:L]; n = n-0.5;
w = [0:1:500]'*pi/500;
Hr = sin(w*n)*d';