Imagine you're filming a car-chase in virtual space.
Doppler effects are very important to make the sound immersive. A car must sound like it zooms by when it zooms by.
But your camera is cutting from place to place, shot to shot, moving at impossible speeds from one shot to the next. Way faster than sound.
So the doppler effect calculations experience a sonic-boom, and every shot-cut is accompanied by a sudden scratch in the sound-track.
What needs to happen is the the doppler calculations are disabled if the camera is moving faster than sound.
But it needs to be disabled *before* the camera starts moving faster than sound. Doing it half way through the move in a frame when the camera's speed goes high is too late. By then the sonic boom is already half way over.
That is the problem I solved yesterday, basically by running a pre-render render and saving a list of notes on when the camera moves.