function [df2,A_sys,b_sys] = ddm_fft_2(win, win_der, mf_ders, sig, N, N_fft, fs)
  R = 2;
  Q = R; % nr of unknows is the same as the number of model funcs, fact!
  [A_sys b_sys] =  ddm_lin_sys_fft(Q,R,win, win_der, mf_ders, sig, N, N_fft, fs);
%    A_sys1 = cat(2,shiftdim(A(1:N_fft-1,1),-2),shiftdim(A(1:N_fft-1,2),-2));
%    A_sys2 = cat(2,shiftdim(A(2:N_fft  ,1),-2),shiftdim(A(2:N_fft  ,2),-2));
%    A_sys  = cat(1,A_sys1,A_sys2);
%    b_sys  = cat(1,shiftdim(b(1:N_fft-1).',-1),shiftdim(b(2:N_fft).',  -1));
%    A_sys = A_sys_;
%    b_sys = b_sys_;
  df2    = lin_solve_dgr_2(A_sys,b_sys,N_fft-1); %hardcoded degree 2 solver (fast)
end