Matching voice timbre from one session to another

As someone that dabbled in audio production whilst playing in bands and recording video, I’ve been helping a friend to produce an audiobook. I’m very impressed with their work, the outcome is very professional. But there are some jumps in timbre and volume between the recording sessions. The same voice, same mic, same room, same equipment, same software, same settings were used throughout, but for one reason and another the results vary slightly. Is there a simple way to tell Audacity to read the frequencies of one file the have it try to reproduce them on another file? And/or is there a simple way to tell audacity to fade the start and end of two files so as to match the amplitude. Normalising the files doesn’t do it because of changes in the dynamic range of the files from one session to another.

There’s normalising, (based on peak levels), then there is RMS normalising, a/k/a loudness normalization.