FPSC cannot scale sounds accroding to distance . However , You can do it manually like this :
:plrdistwithin=450,plrdistfurther=300:soundscale=50,sound=yourpath
:plrdistwithin=300,plrdistfurther=150:soundscale=100,sound=yourpath
:plrdistwithin=150:soundscale=200,sound=yourpath
This is a very simple untested script and it won't play the sound properly but the point is that you should use these commands to check if the player is far , close or too close and scale the sound according to that . You'll have to do the rest
"I am the night visitor when everyone is sleep , and when the last light fades"
The illusionest