Buffer Position and Velocity
As a sound source moves, it is up to the application to specify values for its position and velocity.
Position is measured in distance units along each of the three axes, relative to either world space or the listener, depending on the processing mode.
Velocity is measured in distance units per second along each of the three axes of a vector. By default, distance units are meters. Velocity is used by DirectSound only to calculate the effects of Doppler shift.