I remember when things were as simple as deciding whether you should run your guitar through the flanger before the chorus unit or vice versa. Nowadays the questions get just a bit more involved.
“I’m working with an album that has already been mastered using Pro Tools 3 with L1 and DUY multiband compressor. We are going to add 3 songs and repress the album. I have final mixes as well as masters of the 3 new songs. Unfortunately the new masters aren’t recorded as hot (levels) as the rest of the album. Can I just normalize the new masters to match or will there be a dithering problem? Do you generally normalize, then master or vice versa?”
We’re not exactly sure what you mean by “master” in this context. Normalization is often part of mastering. As a very general rule normalization is done at the end of a project. L1 in particular has different algorithms for use when you intend to do further processing of the signal later. A signal that gets normalized too many times will begin to get grainy and distorted, just like too many passes through a dithering algorithm will produce audible artifacts. Compression, on the other hand, can be done to a signal at multiple stages, but you still have to watch out for a build up of side effects. In this specific case your level discrepancy could be several things. Maybe the solution is as simple as just raising the level. Maybe some mild compression along the way will do it, or maybe you need to slam it in L1. There are no hard and fast rules that apply to every situation, which is why we have studio engineers who know what they are doing. You just have to listen to the material and make a judgement about the best process to bring it in line with the rest of your recording.