Several students have asked questions similar to this:
I have a character listening to a fight in a neighboring room. In order to record this sound, would I record the fight normally and then put some sort of filter on in during mixing, or should I actually record it through a wall?
There are two ways to accomplish this effect.
1. Worldizing, recording the real-world muddy version through the wall. Walter Murch probably created this term when re-recording the music in AMERICAN GRAFFITI.
2. Futzing, which is recording it cleanly, then deliberately messing it up electronically, usually done in the final mix with EQ, reverb and/or delay.
Each has its advantages and disadvantages. Worldizing will sound the most real. However, it is VERY hard to judge how well a sound will work until you hear it in context with everything else in a good monitoring environment. This is the reason we have a mix. So, if you "overdo" the Worldizing, there's no way to undo it. You can always add reverb in the mix, but you can never take it off. Usually, if we Worldize in the real world, we also bring a "clean" version to the dub stage, just in case.
Futzing may not sound as real, but especially if it is dialogue or music, you may not want it to sound real. It may be more important that it is intelligible than realistic. Usually this is the way to go.