I encountered something strange regarding echoes and pitch.
One Fourth of July , I saw rockets reach a height its hard for me to gauge. I'd call it two to three dozen meters.
I had noticed that shortly after a rocket went off, Pop!, I'd hear a Pang! echoed from the wall of a nearby building. The Pang came about a half-second after the Pop. The Pang was little shorter in duration from the Pop and had a higher pitch than the Pop.
That night I was talking to my professor. He pointed out that reflection doesn't change pitch at an interface and said I must be mistaken.
Is it possible I wasn't? Perhaps there is some physical mechanism that would have filtered out the pitches?
Perhaps longer wave lengths were more dampened by the aluminum siding leaving higher intensities for the higher pitches? It was probably a hot day. Perhaps temperature differences could effect the pitches along the direct path differently from those from an echoed path so that there was a different balances of pitches when the echo arrived? A non-physical explanation, my left ear was facing the building the Pops were in the direction of my right ear. Maybe I've lost high pitch hearing in my right.
If this helps, the building was about 5 to 8 m high and Between 10 and 15 m long. The siding had 3cm depth by 3cm width ridges running the height of the side of the building facing the fire works show, periodically.
I'm about 168cm tall. I believe was two times the distance from the fireworks as I was from the building. I was roughly 6m from the building. I was located roughly in the blue location marked ME and the poppers were around SRC in red.