Remember example 1? Then tell me it didn't look like a tennis court. With less reverberation this time a ball bounces back and forth in the room. The impact of the ball against the side walls creates a distinctly noticable stereo effect as the ball travels from right to left. The stereo effect is composed of three phenomena: Interaural intensity differences (ΔI), Interaural time differences (Δt) and an enveloping reverberation in the tail. The ears of the listener are seperated by the size of ones head, which results in the fact that a sound ray might reach one ear slightly earlier than the other. The head mass also attenuates the sounds, which results in intentity differences that differ largely for the subsequent frequency ranges. These effects are obtained automatically by simulating spatial acoustics using Ray-tracing. The notion of stereo is more subtle than simple stereo panning (that is a mere difference in amplitude between the left and right channel), because the early reflections against the opposite walls slightly negate the intensity differences, but induce a more spatial quality to the rendered effect.
The image below features a stereo impulse response of one of the impact sounds on the wall on the left. The red area indicates the sonic energy for the ear on left, whereas the green area accounts for the sonic energy reaching the right ear. Where both areas overlap a yellow blend is displayed. Our perceptive system decodes these cues and reconstruct a spatial impression based on the interaural intensity and time differences.