I need don't know exactly how Doppler Effects can be applied to the background, because when it is used I hear diferent kind of noise and many source are disturbed. Please... send me and example or a code.
To the background? What exactly do you mean by that?
If you set the doppler effect, then its global on all sources, using the velocity of the source or the listener to calculate the effect. So if your sources have velocities applied to them, then it will change frequency