Doppler Factor

DirectSound automatically creates Doppler shift effects for any buffer or listener that has a velocity. Effects are cumulative: if the listener and the sound buffer are both moving, the system automatically calculates the relative velocity and adjusts the Doppler effect accordingly.

In order to have realistic Doppler shift effects in your application, you must calculate the speed of any object that is moving and set the appropriate velocity for that sound source or listener. You are free to exaggerate or lessen this value in a particular case in order to create special effects. You can also globally increase or decrease Doppler shift by changing the Doppler factor.

The Doppler factor can range from DS3D_MINDOPPLERFACTOR to DS3D_MAXDOPPLERFACTOR, defined as 0.0 and 10.0 respectively. A value of 0 means no Doppler shift is applied to a sound. Every other value represents a multiple of the real-world Doppler shift. In other words, a value of 1 (or DS3D_DEFAULTDOPPLERFACTOR) means the Doppler shift that would be experienced in the real world is applied to the sound, a value of 2 means twice the real-world Doppler shift, and so on.

The Doppler factor can be set and retrieved by using the IDirectSound3DListener8::SetDopplerFactor and IDirectSound3DListener8::GetDopplerFactor methods.