  Geometrical acoustics is well suited for simulating room reverberation in
interactive real-time applications. While the image source model (ISM) is
exceptionally fast, the restriction to specular reflections impacts its
perceptual plausibility. To account for diffuse late reverberation, hybrid
approaches have been proposed, e.g., using a feedback delay network (FDN) in
combination with the ISM. Here, a computationally-efficient, digital-filter
approach is suggested to account for effects of non-specular reflections in the
ISM and to couple scattered sound into a diffuse reverberation model using a
spatially rendered FDN. Depending on the scattering coefficient of a room
boundary, energy of each image source is split into a specular and a scattered
part which is added to the diffuse sound field. Temporal effects as observed
for an infinite ideal diffuse (Lambertian) reflector are simulated using
cascaded all-pass filters. Effects of scattering and multiple (inter-)
reflections caused by larger geometric disturbances at walls and by objects in
the room are accounted for in a highly simplified manner. Using a single
parameter to quantify deviations from an empty shoebox room, each reflection is
temporally smeared using cascaded all-pass filters. The proposed method was
perceptually evaluated against dummy head recordings of real rooms.
