Dirt-Cheap 3-D Spatial Audio   Many computer systems set up for
advanced gaming include Dolby Surround Sound. The typical
speaker configurations are 4.1—four speakers and one subwoofer—
5.1 and 7.1. This system is designed for all speakers to be
located on a plane centered at the listener, and thus it is not
possible to have a sound truly be emitted from above or below
the listener, although some systems attempt to simulate that
effect. Imagine a game scenario where a monster is climbing down
a wall above and behind the player while, at the same time, a
mouse is scrambling across the floor behind the listener. In a
planar surround system, the sound effects for both the monster
and the mouse would come from the rear speakers, making it hard
to distinguish the actual locations of the sound sources.  With
true 3-D spatial audio, the monster's sound effects could be
played from speakers located to the back upper-left and the
mouse's sound from speakers located to the back lower-left and
back lower-right. In this