  We study the propagation of light pulses in an absorbing medium when the
frequency of their carrier coincides with a zero of the refractive index
dispersion. Although slow light and, a fortiori, fast light are not expected in
such conditions, we show that both can be obtained by selecting particular
phase-components of the transmitted field. Analytical expressions of the
resulting signals are obtained by a procedure of periodic continuation of the
incident pulse and a proof of principle of the predicted phenomena is performed
by means of a very simple electrical network, the transfer function of which
mimics that of the medium.
