A/D converters DO have a sort of "sweet spot", meaning, a level where they sound their best. Bit resolution isn't the ONLY defining aspect of A/D's.
With that in mind, on certain things, you may want to keep your recorded track within a level range on the A/D, and for some singers, a compressor might be the only way you can achieve that.
The trick to tracking vocals with a compressor is to make sure you use a pretty low ratio (2:1 or less), and a long release time (at least 500ms, but possibly more like 1500ms!). Probably won't be so good to do NO MORE than 6dB of gain reduction at any point.
These are very general settings. I have done differently with good results.
The bane of matching analog gear and digital gear is that they behave almost exactly opposit of each other in regards to distortion.
Analog will distort more if levels are really high. Digital will distort more if the levels are really low.
So, if we turn down our preamp, and keep it out of any possibility of producing distortion, we produce low levels going to the A/D converter. Low levels at the A/D converter means more distortion from the quantization errors.
Inversely, running the preamp hot will produce more distortion, but the A/D converter will of course will not produce distortion from Q errors.
Somewhere in the middle, we have to work.
