Every mastering engineer has their own little quirks about their preferred Peak dB levels and what kind of effects are acceptable on the master bus aka mix bus. For the purpose of this blog, we will go over some general rules on preparing your pre-master mix for the mastering stage.
What effects are ok for the master bus?
Every audio effect that makes the mix sound the way you want it to sound is just fine for the master bus. With that said, you do not want to squash the hell out of your mix with the use of compressors and limiters. I would actually go as far as to say leave all limiters of the master bus and if you want to use compression, please use it very mildly. This is because the mastering engineer will be using compressors and limiters and he will not be able to undo the mistakes you may have made by over compressing the mix.
An example of some of the mistakes that you can make using the compressor are:
Setting the attack time to fast or slow. This can take the punch out of your song.
Having the release time too fast or too slow. This can lead to not having the compressor catch the transients that it needs to.
Setting the threshold too low or high. Having this setting not to the correct level can do massive damage to your pre-master mix. Especially if its t low.
The ratio setting being too aggressive can lead to a lifeless sounding mix.
All those things above cannot be fixed in the mastering stage. So my advice is to leave compressing and limiting to the professionals.
Example of an Audio Compressor
What dB levels to send?
We like to have the mixes anywhere between -16dB to - 3dB Peak. As for the RMS levels, you really do not need to worry about them. Just worry about getting the mix to sound the way you want it to sound. The RMS and LUFS levels do not matter because you are not taking the mix to its desired listening level in the mixing stage. You are just leveling each track, panning and creating a nice stereo filed and adding effects on the track level and bus level. Doing all that, you are creating the sound you want without worrying how loud it will sound on all the different sound systems
What sample rate and bit depth?
Changing the sample rate and bit depth requires conversions that should not be done. This means that if you created a new project in your DAW record and mix in, then the sample rate and bit depth was defined there as well. You should always keep the same settings for those two things. If your Cakewalk, Logic, Pro Tools or Cubase project, to name a few, is set at 24bit / 96kHz, then you export the wav file at those same settings. Never convert down or even up. There is one exception. you can convert up to a floating bit depth of 32 if your project is 24bit and when you export the mix for mastering, you can export it at 24bit and whatever the original sample rate was.
Are MP3's good for mastering?
Hell no! With one exception. If you lost the wav or AIFF file and you do not have access to the project to export a wav file or AIFF, then there is no choice and the mastering engineer will do his best. But if you have access to the exported wav files, MP3's have no place in the mastering stage.