How do I turn off Sample Rate conversion in Au?

r2-no-d2  wrote Other programs do not make unnecessary copies of files. Reaper does this on the fly and does not create a bunch of unnecessary files in the project folder.

Audition doesn't either. It assumes (quite reasonably) that you may not finish all your work in one go, and saves you having to go through the whole process again when you restart. The other important thing you have to bear in mind is that all sample-rate conversions on the fly are, at best, of dubious quality, as they rely on the OS to do this. Audition doesn't - it uses its own SRC, and this has been independently rated as being about the best there is - regardless of what you pay. File space these days is cheap, and Audition is actually doing you a favour here, despite you not appearing to appreciate it...

Sessions in Audition can only work at one sample rate as defined when you start a new Multitrack Session. So SRC can't be turned off since Audition needs to match the imported to the session rate if they are not already at the correct rate. Normally a new session would be started with the correct sample rate for the audio that is going to be used for that session.