[GraemeJ]

Firstly, you can not do this within MSP, it will have to be done using an external program.

Secondly, you have to understand that 'normalising' an audio file merely increases it's level such that the peak level is at 0db (or whatever peak level you choose).  If that's what you need to do, then fine, but what most people need is to make a series of tracks play at the same relative level.  If you 'normalise' a series of files, their relative volumes will still vary - you need to to do something known as RMS (root mean square) balancing, this makes all the files play at the same relative volume.

There's a ton of programs around that can do this, from free to expensive.  You can search for them easily enugh, but I'll give you two to start you on your way.  For .wav files, volume balancer - http://www.delback.co.uk/volbal/ - and for MP3 files, MP3Gain - https://www.filehorse.com/download-mp3gain/ .