  The one-dimensional propagation of waves in a bichromatic potential may be
modeled by the Aubry-Andr\'e Hamiltonian. The latter presents a
delocalization-localization transition, which has been observed in recent
experiments using ultracold atoms or light. It is shown here that, in contrast
to Anderson localization, this transition has a classical origin, namely the
localization mechanism is not due to a quantum suppression of a classically
allowed transport process. Explicit comparisons with the Anderson model, as
well as with experiments, are done.
