TL;DRAdd API for mods to change the volume and radius of sound effects.
What?The volume of sound effects can currently be changed manually by the user by replacing game files with louder versions of those game files. Mods can also replace sound files.
What mods cannot do is adjust the volume of those sounds in-game, or adjust the radius from which they can be heard.
Why?Sounds can be heard from different distances - for example, inserters can be heard from a few tiles away, whereas belts can only be heard if you're very close to them - after all, you wouldn't want your eardrums pierced every time you crossed your main bus.
However, I'm not happy with the distribution of sound volumes and sound radii in-game. Take trains for example. When riding a train, I struggle to hear the thrum of the engine, and yet the clack-clack of traversing the track is very loud. I would like to increase the volume of the train engine, and also increase the radius from which the train can be heard - I want to be able to hear these massive engines even when they're off screen!
Currently, mods offer no way to do this, hence my suggestion.