Don't know how many of you follow the progress of video / animation development, but
Blender has a GSOC project involving 3D audio. It includes things such a audio sources
moving in
3D space as well as things like the doppler effect for moving audio sources. There is an
iteresting video demonstrating the current progress.
http://www.blendernation.com/2011/07/30/gsoc-2011-3d-audio-tools/
-Reuben