傅立叶时移在Matlab fir2（）函数中起什么作用？
我在理解Matlab信号处理工具箱fir2（）函数中的一些代码片段时遇到问题：傅立叶时移在Matlab fir2（）函数中起什么作用？,matlab,signal-processing,fft,Matlab,Signal Processing,Fft,我在理解Matlab信号处理工具箱fir2（）函数中的一些代码片段时遇到问题： % My comment: at this point vector H contains nn+1 (nn is an even number) points (double numbers) of amplitudes for a dense frequency grid % Fourier time-shift. dt = 0.5 .* (nn - 1); rad = -dt .* sqrt(-1) .*
% My comment: at this point vector H contains nn+1 (nn is an even number) points (double numbers) of amplitudes for a dense frequency grid
% Fourier time-shift.
dt = 0.5 .* (nn - 1);
rad = -dt .* sqrt(-1) .* pi .* (0:npt-1) ./ (npt-1);
H = H .* exp(rad);
%My comment: now H contains nn+1 complex numbers
%My comment: creates a horizontal mirror with 2*nn points
Hconj = [H conj(H(npt-1:-1:2))]; % Fourier transform of real series.
ht = real(ifft(Hconj)); % Symmetric real series.
%My comment: throws away the half after ht[nn]
b = ht(1:nn); % Raw numerator.
wind = hamming(nn);
b = b .* wind(:).'; % Apply window.