Mastering is not about loud!
There is an unfortunate preoccupation on the part of some people with making their recordings loud. Some of it is understandable, we all want our recordings to sound comparable in loudness when played alongside other music. But things have been carried to the extreme! If you look at the wave forms for many tracks, they are completely maxed out and squashed. I have even seen tutorials that actually claim that mastering is all about making your recording as loud as possible!? No, its not.
Mastering is about three things. One, correcting minor flaws to make the track sound as good as possible. Two, evening out the volume of each song on an album so that they all sound consistent when played together. Three, putting the songs in the order that works best for that particular set of songs. And most of the attention and skill is applied to number one.
Notice that loudness is only a secondary consideration for the mastering engineer. In fact, making all the songs on an album sound at the same relative loudness could actually involve turning the level on many of them down!
Mastering is about making each song sound as good as possible by itself. And, then making all the songs on an album sound good together. And mastering enginners have the knowledge, the experience, and the gear, to accomplish that.
Never lose site of the fact that everything we do is in service to the music. Simply making a song louder is not necessarily an improvement. The idea is to have all the tracks we record sound as good as possible! In fact, if we do our job of recording and mixing really well, then no mastering is required at all!
Believe it or not, there are recording and mixing engineers who do their job so well that their finished mixes require no mastering. And , yes, there are Grammy winning "Best Engineered" albums that needed no mastering. Sure, they are exceptions, but they show that it is possible.
Of course, mastering engineers are very much aware that the track needs to be similar in level to other songs in the same genre. But, just cranking everything up is not necessarily required. As one engineer puts it ( and I think it was Bob Katz), "it is not how loud you make it, it's how you make it loud".
And this gets us to the technical part. Just how do you make it loud? And while there is no one specific answer to this question, think in terms of contrast. In other words, remember that in order for something to sound loud, it has to also contain something soft. Yes, that is where the magic is. The magic is in having a soft part to compare with the loud part. If everything is "loud", then the listener might simply turn it down. But, if it has soft parts too, then they need to maintain some level in order to hear the soft parts, and so when the loud part of the song occurs, it stands out!
The bottom line is here is that the perceived loudness of your track is actually the difference between the loud parts and the soft parts (called the dynamic range). That is the trick! And you do it with judicious use of compression, and perhaps a little limiting to prevent overs (clipping). You do not push everything as hard as possible in the limiter. No. That only makes things sound squashed, and what some engineers call "pre-distorted".
So preserve the dynamic range of your tracks. Use compression to bring out the amount of level that each track needs. Then a touch of limiting to make sure nothing is overly loud.
See, we've turned it all upside down. Now the limiter is there to prevent things from being too loud, not to make them loud. Making them loud happens in the way you manage the dynamics, the loud and the soft, of your track to make it sound as good as possible, and consistent with the genre.
Now you know. Professional mastering engineers are very good at what they do. But, making your music louder is not what they do. What they do is to make your music sound better. Louder has to be built-in to the way the track was mixed. And the limiter is the tool of last resort.
All of this is good to know since many of us are in the position of needing to do our own mastering. And maybe we will never be as good as the professionals. Only time, and experience, and practice, practice, practice, will decide that. But at least now you know where to start.