Desired Impulse Response

h = ifft(H); % zero-centered form

% rough estimate of time-aliasing error:
aerr = norm(h(N/2-N/32:N/2+N/32))/norm(h)

aerr =
   4.8300e-04

% for plots, prefer negative times on the left:
hp = [h(N/2+2:N), h(1:N/2+1)];