I have been very pleased with Ardour - only took me a few minutes to have my XLR mic go through a compressor / limiter / expander virtual rack effects setup for better screencasting.
He's trying to make his audio easier to listen to by using various effects provided by Ardour. The most significant of what he listed is the compressor, which is great for spoken podcasts. It will take any sound that is over a certain threshold and start to to reduce it's volume (eg. compress it), so if he's talking really quietly and then yells something really loud, the person listening isn't subjected to as large of a volume range in their ears.
The limiter just limits the maximum volume, and I'm not sure why he's using an expander.
I'm not sure I understand the point of using an expander after a compressor as one reduces the dynamic range but the other increases it again. What about a little eq cut/boost instead?
Sorry I still don't get it. That thread explains some uses for expanders, just not after compressor or limiters in the same effects chain. Surely if you need an expander after a compressor then you've got your setting wrong on the compressor, or maybe you need a noise gate before it.
I've used it for recording music, combining some MIDI tracks with many audio tracks and samples. Once the audio system was set up and stable, working with Ardour was a pleasure and results were very good.
The main problem was getting high quality effects/plugins, paid or free. There are a couple, but in general life is much easier in this sense outside of Linux. That was 2-3 years ago, and hopefully things have improved since.
Those were the main ones I worked with, plus another commercial package, I forgot its name, which was decent.
The Calf compressor and bass enhancer were very good. I'm seeing that a lot of plugins have been added in the time since I last worked with Ardour. Makes me want to start making music again :)
Unfortunately, the CALF series have been notorious for having problems or causing crashes in the past. If you do want to try it out, I highly recommend getting the latest version or building from git as a lot of distributions package an older version in their repositories.
Things are slowly getting better if you want to run Windows VSTs under Linux. I found this very interesting as a overview of some of the current possibilities: https://www.youtube.com/watch?v=jsZnSg4DKDU
It is a demonstration for a proprietary DAW, Bitwig, but he does talk a lot about Windows plugins under Linux that I imagine applies to Ardour as well.