  We investigate anomalous energy transport processes in the Fermi-Pasta-Ulam
$\beta$ lattice. They are determined by the maximum sound velocity of the
relevant weakly damped energy carriers. That velocity can be numerically
resolved by measuring the propagating fronts of the correlation functions of
energy/momentum fluctuations at different times. The numerical results are
compared with the predictions for solitons and effective (renormalized)
phonons, respectively. Excellent agreement has been found for the prediction of
effective long wavelength phonons, giving strong evidence that the energy
carriers should be effective phonons rather than solitons.
