I think the existing answer is good and doesn’t go far enough.
First, I would suggest you put zero plugins on your master output track or stereo bus or whatever you want to call it. For two reasons:
- It will help you make a better mix, since you’ll have to make things work without processing on the stereo bus.
- It will let your mastering engineer do what they do best.
Second, when you’re looking at your stereo bus levels, one important thing to pay attention to is crest factor. Crest factor is the difference in dB between the average (usually RMS) and peak levels. A recording is “bricked” when it has less than say 6dB for a crest factor, although many recordings you hear have between 3 and 6 dB for a crest factor. The worst examples have close to 0 dB. Feature films are usually delivered with a crest factor of about 20 dB, and that’s after they’ve been mastered. Many of the best sounding music recordings will have a crest factor of about 12 dB, but remember that’s what your mastering engineer is going to deliver back to you.
I strongly suggest not spending any time reducing the crest factor on your stereo bus to less than 20 dB. That means since your peaks are supposed to be no higher than -3 dBFS, your RMS levels would ideally be no higher than -23 dBFS. Check your DAW’s manual to find out how to configure your meters to show RMS levels. Most can show RMS and peak at the same time.
Critical note about delivering to streaming services
Most of the major streaming services, including YouTube, iTunes, and Spotify have reduced output levels and are recommended crest factors of at least 14 dB when you deliver your master to them. If you or your mastering engineer reduce your crest factor below 14 dB, it will actually sound quieter when streamed, not louder. You should ask your mastering engineer about that if you want to deliver to streaming services and of course your can’t create crest factor, only reduce it, so you definitely should send a crest factor of at the very least 14 dB to be mastered.
Also, one could argue this column by mastering engineer Bob Katz was the first shot fired in ending the loudness wars, and his K-system that he proposes here is now widely used: