Real time audio normalisation / limiting
Solution 1:
OK, so just for other peoples benefit, this is the best solution I have found myself:
A program called PulseEffects. its GUI based and runs as an application so its easy to start and stop without having to fiddle with config files. It also allows you to easily stack multiple effects, like compression, automatic gain, a limiter etc and you can apply it application by application, so if you want it on for Chrome but not spotify thats easy to do.