Something called CD mastering is one of the best secrets of high-end mixing engineers today. Since most everything is mixed in the digital realm, highend mixing engineers will do what’s called analog mastering. The digital version is put back to an analog signal in order to be mastered through original analog processors, though in many instances it is also recorded to an two-track system in order to get the richness that analog tape gives to the project. It also takes the edge away from digital recordings, and can even out the bottom end giving the bass frequencies that nice analog sound.
Analog mastering can cost a bit more than traditional all digital mastering, since it takes additional time and there are the costs for the analog tape, but for serious projects, it can be the end step in getting the top quality for the project. Since digital recordings can feel harsh to many people because no matter how loud the sound gets, digital always gives you accurate yet flat reproduction. Analog tape, on the other hand, softens as the volume increases in level, so heigh end peaks are smoothed over instead of clipping, which turns into a warm, fat feel as the harmonics are balanced out. This is much more pleasing. Also, a hotter input signal will result in a more exaggerated effect. Since the top ranges soften up first, this transilates that as the signal increases, the highs naturally smooth out a bit, resulting in a less harsh, nicer sound. This is the beauty of layback mastering.
There are several mastering studios around the United States that have the equipment to do analog mastering, however, it also necessitates you have a solid professional with the background to get the best results possible with the studio. I have tested out a few mastering studios and one of the most impressive is www.stevethomasmastering.com. He is a top analog mastering engineer, yet he also has done 1000s of albums as a recording engineer as well. On top of that, his results rivals some of the most expensive mastering houses in the world. If you already have someone you are using that’s great. But, I would certainly to look him up.