Watsisname wrote:Source of the post I plotted its spectrogram
Nicely visualised. Same thing visible in the spectrogram of the meteor sound.
Now thinking aloud:
The object is decelerating. Before the sonic transition it leaves a trail of ripples moving slower than the object, so the object is outside the ripples. As it approaches the sonic transition point, the lower part of these ripples become closer and closer, then they pile up at the transition point and as the object decelerates further inside the ripples they become more and more spaced again. The packed ripples will reach the witness first, whether they were emitted before or after the transition. I think that holds regardless of the relative position of the witness, but perhaps how rapid the pitch falls can hint the angle between the meteor and witness, if we know the deceleration rate.
This could probably be effectively visualised in an animation, but that takes a bit of work.
As for the Mythbuster video, maybe there is some initial supersonic expansion, which quickly goes sonic, and what we hear is that expansion approaching sonic speed, reversed.