A personal addendum on the subject of mastering 

"In my opinion, the process of mastering is quite underestimated nowadays (like perhaps the whole art form of music). After all, what is mastering actually about? 
Well, of course, there are often technical corrections to be made and compatibilities to be maintained. That's where an AI or new types of plug-ins can certainly do a great job. 
But what about the essence of the music? The intention, the artistic message and the emotionality? In my work as a mastering engineer, sometimes the "technical error" was exactly what enhanced the intention and underlined the artist's work. 
And self-mastering also remains to be questioned. What is missing is objectivity (as far as one can speak of it at all as a human being), the "second opinion", the review on another, often much more accurate listening situation. And the personal consultation is another very crucial point. In some cases, a slight revision of the mix has led to a much better result than any intervention on my part. Not to mention a learning and experience process for the artist.
But also the artistic input of the mastering engineer, who should always try to enhance the fundamental things of the music as much as possible and transfer them to any listening possibilities. The intention, the artistic message and the emotionality!
And that is exactly what I see as my passion. Every conversion, every piece of hardware, every plug-in and even every cable has been checked, scrutinised and confirmed in (blind) tests countless times by me - and even anew with every new order, in order to guarantee the best possible sound. Hence all the hype about equipment in studios. Only the best is good enough for everyone's valuable, artistic work! I usually had the impression that cheap equipment - but above all the wrong use of it - can virtually suck the emotionality out of the music.
One would like to think that there are more important things nowadays, especially in these times and with the prices for good hardware. I, too, have often asked myself that. But to appreciate, preserve and support the artistic heritage of every person/artist must simply be and remain important!
And another addendum: As in hardly any other field, there is "no right or wrong" in music. Personal taste is decisive, but as mentioned above, so is the intention, artistic statement and ultimately one's own feelings. After all, every person hears differently, purely biologically and mentally. So what is supposed to be right or wrong? And as mentioned, exactly one objective "technical error" can underline your statement and intention.