DirectSound applies Doppler-shift effects to sounds, based on the listener's velocity in relation to one or more 3D sound buffers. DirectSound can apply to a sound up to 10 times the Doppler shift experienced in the real world by setting a Doppler factor. To set this factor, use the IDirectSound3DListener::SetDopplerFactor method. The Doppler factor can range from 0 to 10. A value of 0 means no Doppler shift is applied to a sound. Every other value represents a multiple of the Doppler shift experienced in the real world. In other words, a value of 1 means the Doppler shift experienced in the real world is applied to the sound; a value of 2 means two times the Doppler shift experienced in the real world, and so on. To retrieve the Doppler factor set for a 3D listener, use the IDirectSound3DListener::GetDopplerFactor method.