You know how in Halo 3, when someone fires an assault rifle or battle rifle from a distance, it sounds different from if you were to heard it up close? Well I found a way to mimic that. Just follow this tutorial.
Step 1: Compile your distant firing sound(s).
Step 2: Open the tag up in Guerilla or the likes.
Step 3: Modify the "Minimum Distance" and "Maximum Distance" to your likings. (For my tags, I put a minimum distance of 30-50, and a maximum distance greater than 100.)
Step 4: Save the sound tag.
Step 5: Open up the firing effect tag for your weapon. (In this case, "tags\weapons\assault rifle\effects\fire bullet.effect") Then duplicate the normal firing block, and reference in your distant firing sound tag.
Step 6: Save the effect tag.
Step 7: Compile your map.