On New Years Eve, I enjoyed a fairly quiet night (I could actually see the street through the smoke), but we could still hear the larger fireworks echo through the valley. The sound waves emitted from the firework is sent throughout the valley, bouncing off anything and everything. I'm not sure you can see anything in this clip, but the flash from the various explosions always came a bit before the the actual sound, depending how far the actual explosion was from our location (From across the street to the firework shows at various hotels).