Thank you for the very clear instruction on how to change the files! There is one thing that is not clear for me though. You say that most sliders in the static attenuation are on the right, but I see them in the left, with a -0 db and if I move the slider to the right I can see the value becoming more negative. Is this right?
Also what would be a recommended value in db to move the slider to, since I've never played with these settings until now?
No, if it's at 0 db already then you can't maker the sound louder without changing the wav files. But most of the regular ambient sounds are not at 0 db, like birds, crickets, wind and tree sounds etc. They all have negative db (at least the ones I checked). Recommendations are impossible as every sound is different (both the source wav volume and where/how it is used). Just look at the db rating and increase it by a few percent. Like if it was at -25 db set it to -20 db, if it was at -10 db set it to 8 db and so on. Maybe go through the sounds by category and test in game so you know what to change if you think the sounds are too loud now or still not loud enough. For example alter all bird sounds and listen to them in game, if you like what you hear change the wind sounds etc.
I know that the annoying creaking sound in Nehrim was changed from -25.99 in vanilla (very subtle, hard to hear at all if you don't pay much attention to it) to something like -11 in Nehrim (very loud).