  We present an investigation into effects exhibited by the two-frequency
kicked rotor. Experiments were performed and in addition quantum and classical
dynamics were simulated and compared with the experimental results. The
experiments involved pulsing the optical standing wave with two pulsing periods
of differing frequencies and variable initial phase offset. The ratio of
pulsing periods was sampled for rational and irrational values for different
experimental runs. In this paper we present these results and examine the
measured momentum distributions for the cause of any structures that are seen
in the energy as the initial phase offset is changed. Irrational ratios exhibit
no significant quantum effects, whereas rational ratios show dynamical
localisation (DL) for certain values of the initial phase. However, most of the
observed structure is found to be due to classical effects, in particular KAM
boundaries, and is therefore not of uniquely quantum origin.
