Ok let’s just put this one to rest in one simple sentence. Below 0db be it -1db or -12db is perfectly fine. There are so many producers out there arguing with each other and following what they have been told like it is gospel. You send a mastering engineer a fully dynamic mix at -3db it’s perfect. You send a mastering engineer a fully dynamic mix at -6db it’s perfect. -12db is perfect. -24db is also perfect. There is nothing wrong with leaving lots of headroom. There is however a great deal wrong with leaving no headroom.
Headroom is required to be left for a number of reasons. The main reason being, a full dynamic range and no clipping or distortion. The reason a mastering engineer will ask for the mix not to be limited or overly compressed is so that he or she has a full dynamic range of audio to work with. By applying limiting or hard compression to the mix bus you will limit the dynamic range. Any distortion applied to the mix prior to mastering will only become more apparent once mastered.
Every engineer will have a guideline to following which is usually -3db or -6db. For myself here at Audio Animals I set the guideline at -3db. The reason for this is it gives ample headroom for the producer to still have a loud mix, whilst enough of a cushion that you will never exceed 0db. As long as you the producer do not exceed 0db the mix will have plenty of hearoom. If you were to send a mix that has -12db headroom instead of -3db, we can adjust the volume of the audio source inputting in the analogue signal chain to increase it to required volume.
The overall conclusion of the often worrying debate of how much headroom should I leave is……..
Below 0db = GOOD
Above 0db = BAD
A mastering engineer worthy of that title will be able to work with any audio source that has below 0db of headroom.