Winamp reverb
 

Hi, I'm looking for a plugin that adds reverb just to the midi files (or just to a certain folder with midi files).

Possible?

No ... MIDI is not audio, it just tells a MIDI device (your sound card, 99% of the time) what to play. You'd have to see if your sound card supports reverb on its MIDI synthesizer.

Yes... it is possible (at least to some extent).
The default (input) midi player plug-in (by nullsoft) supports applying reverb, although the feature may require that your midi device supports reverb.
To enable it, just hit configure on the "Nullsoft MIDI player", go to the DirectMusic tab, and check reverb.

The setting cannot auto adjust, based on the directory of the currently played file though, and if you want to add reverb to the physical midi file (and not just apply reverb when playing the file), you will have to sample the midi file and save it in a "real" audio format (which will probably reduce quality or severely increase the files size, but allow you to modify the output in the usual way). It may also be possible to add reverb to the midi file using a midi composer, but I don't know anything about those.