Spatial Parameters of the Listener
Like a sound source, the listener has a position, orientation, and velocity in the 3D world.
The orientation of the listener is defined by the relationship between two vectors that share an origin at the center of the listener's head: the top and front vectors. The top vector points straight up through the top of the head, and the front vector points forward through the listener's face at right angles to the top vector, as in the following illustration.
Figure 1. Listener_vectors
By default, the front vector is (0.0, 0.0, 1.0), and the top vector is (0.0, 1.0, 0.0). The two vectors must always be at right angles to one another. If necessary, DirectSound will adjust the front vector so that it is at right angles to the top vector.
Position is measured in distance units along a vector.
Velocity is measured in distance units per second along a vector. By default, distance units are meters. Velocity is used by DirectSound only to calculate the effects of Doppler shift.