The Effect is called Doppler Shift... An Example is of a Big Rig Truck Honks his horn from behind you its higher in pitch but when passing you it lowers in pitch....QuantumCurse wrote: ↑Fri Sep 30, 2016 9:00 pmIt could also be taken into account that the 612s rotate so the sound will sound different when the siren head is on axis with the camera microphone. Don't know how true this is but it's a possibility