In the ergodic capacity literature, the majority of results preserve the assumption of a flat-fading Gaussian channel. However, the actual wireless channels in current communication systems are often wideband and therefore time dispersive and frequency selective. In this direction, we study the ergodic capacity of a wideband MIMO channel. Starting from a tapped delay line model for the time domain, the frequency domain model is derived by employing the Fourier transform. However, in both cases the resulting channel matrix is characterised by non- separable correlation amongst the Gaussian blocks. The asymp- totic eigenvalue probability density function and the channel capacity are calculated by specializing a theorem originating in operator-valued free probability. Finally, numerical results are presented to verify the validity of the approach and study the effect of the channel model parameters.