用matlab写一段SPA滤波函数

function [y] = SPA_filter(x,fs,f0,df,Q)
%SPA_filter Summary of this function goes here
% This function implements a single-pole all-pass (SPA) filter.
% x: input signal
% fs: sampling rate
% f0: center frequency
% df: frequency deviation
% Q: quality factor

% Calculate the filter coefficients
w0 = 2*pi*f0/fs;
w1 = 2*pi*(f0+df)/fs;
w2 = 2*pi*(f0-df)/fs;
a0 = tan(w1/2)-tan(w2/2);
b0 = -cos(w0);
c0 = 1/tan(w1/2)+1/tan(w2/2);
d0 = 1-c0/2;

% Initialize the output signal
y = zeros(size(x));

% Apply the filter to the input signal
for n = 2:length(x)
y(n) = a0*(x(n)+x(n-1))-b0*y(n-1)+c0*x(n)+d0*y(n-1);
end

% Normalize the output signal
y = y/max(abs(y));

end