A huge part of Quantum Mechanics is Conservation of Information, or better maybe to think of it as a conservation of entropy?

Your example of a soundwave is too local in scope, sure the wave will die down, but while the soundwave was propagating it's bumping into other particles and those particles affect other particles, which affect other particles, and on and on and on.

If you look locally, sure, eventually you wouldn't be able to tell the wave ever existed, but if you pull back far enough and take the state of the system and rewind it you will eventually reconstitute the wave.

Your example with annihilating particles is basically how CERN works, though we do know what we started with in some places.

I had started to describe the whole of how Hawking Radiation works, I'm sure you can find that easily elsewhere.