Doppler.

Doppler recreates the pitch shift a sound undergoes as it passes you, the effect behind convincing fly-bys, passing cars and trains. A display shows the path the sound takes, so the movement can be shaped rather than guessed at. A reverb tail generator adds the reflections that place the event somewhere real, and Air Damp models the high-frequency loss that comes with distance. It works musically too, on percussion, guitars, synths and backing vocals.