function R=spec2fir(A)
% SPEC2FIR: convert magnitude spectra to FIR filter coefficients
%
% spec2fir :: [[M,L]] -> [[2*(M-1),L]].

n=size(A,1);
S=[A; conj(A(n-1:-1:2,:))];
R=fftshift(real(ifft(S)),1);	% get filter coefficients

