Sorry this might be a long answer because you mentioned mastering in the question and I had a few decisions to make regarding that, specifically for this album
Everything was pretty much done by ear during performance. There’s a few things I’m doing per song, so there’s a lot of multitasking going on. The monome / Arc is front and central, so I am playing them and triggering patterns. In the middle of the actual case there is a submixer that everything is going through which I use to fade in and fade out different sections by hand. At the same time my right hand is also live looping with a W/ on the far right end of my case. My left hand on the far left is on a Count to 5 for live looping and 2 Eventide pedals. I have presets on the Eventides set per song, a little bit like a guitar player does. So my stance is bit like a pinball machine player looking at the cockpit of of 737 whilst juggling
Playing this music live in a club sounded fine but mastering that sound into an album was tricky. I initially mastered the album myself but was never really happy with the results and partially because my studio room / speakers are not sufficiently treated for bass and it’s a small boxy room. To confirm my suspicions I posted those masters to a few friends and asked them to make technical comments and if they could hear certain things. They couldn’t. With those comments from friends I sent the album out to be properly mastered and EQ along with comments made by my friends per track plus a comparable YouTube/Bandcamp link per track of a professional artist whose sound I liked, that related to that track. The main issue was not hearing the bass and EQ’'ing on certain tracks with multiple synth lines. The other issue was dynamics which I knew my mastering lacked.
My previous albums were done on an Easel and Serge and i mastered myself. Those were pretty easy, as they are systems that are voiced and EQ’d already, the dynamics are fine and I knew from the start the sound eq / bass was fine when I sent versions to friends. With this Eurorack system, the voicing is very different and mixed up, different modules, live looping, multiple synth melodies and I’m using samples also from the er301. It’s a lot more tricky to master correctly, that’s the reason I had it done professionally.
The chose of the mastering guy was important. They will colour your sound with the way they work, their techniques and equipment and they will put their stamp on your music. It’s very much a personal thing about who you choose as they all have their own strengths.
I asked a mastering engineer friend if he could recommend anyone initially and I also looked at other recommendations in the mastering thread on here but they weren’t quite what I was looking for. There’s a certain type of sound and vibe I’m going for that’s difficult to explain but I can tell very quickly whether it’s for me or not. For me it’s like dialing in a sound, I know straight away whether it’s for me or not. I’m pretty clinical when it comes to knowing what sound I like.
In the end I used my ears and listened to lots of records that i physically owned that I liked the sound of, then looked at who mastered it on the back cover after I listened
If I like the sound of the mastering guy, I go a bit deeper and start to look for more stuff they have mastered and particularly before and after samples. I also look at the equipment they are using, the studio setup, particularly the monitors and specific mastering outboard gear they use and whether it is something similar to what I use. But really, it’s not about the gear, that’s a more secondary thing, after like the sounds. There’s certain mastering guys with brilliant studios but not that keen on the sound they are going for. So it’s mostly about the person and what your ears are telling you.
The other thing was I’m not bothered if they have mastered lots of electronic named artists or particular modular artists before. Because of the variety of material on the album I needed to find someone who had worked with a wider range of material. I more look at the wide range and variety of stuff, something from West African, Ambient, Folk, Pop, Thrash Metal, Hip Hop, Country and Western, Indie, as well as the more electronic side. I do this as some of the best mastering guys, master stuff I don’t necessarily listen to.
Sorry for the long answer!
I also wrote a couple of things about both the way I play live Performing Modular Live and also the way I record a modular album Executing the modular album I think they are both interchangeable and valid for this particular album