Replicating Audacity's "soft limit" function

And not to take the tools in a vacuum, AudioBook Mastering 4 combines three tools into a suite.

Effect > Equalization runs a rumble filter to eliminate room and microphone error rumble.
Effect > RMS Normalize to set overall RMS (Loudness).
Effect > Limiter to clear up any peak errors.

If you recorded in a quiet room, you’re done.

The suite is applicable to many different recording techniques and can’t be heard working in normal operation.

https://forum.audacityteam.org/t/audiobook-mastering-version-4/45908/1

Koz