The loudest part part of your mixed song should be below 0db level. “0db” level is the clipping point, having space between the clipping point and the music allows the mastering engineer to manipulate the sound. The ideal amount of headroom would be +6db (a level of -6db below 0db level). Be sure to never let your levels go over 0db on any of your tracks, doing so will not leave any room in the mix for the mastering engineer to work with. Loudness maximization is done in the mastering process, there is no benefit in having your music go over level in the mix. **Occasionally you can peak at 0db level or slightly above for quick hits such as a snare or hi hat as long as they don’t distort, however it is beneficial for you to leave space in the mix to achieve the best master possible**
This has about +6db of headroom
This has about +3db of headroom
This peaks at 0db, but has no clipping
This example is +3db over level, the flat spots indicate clipping and distortion
This is +6db over level, shows clipping and distortion.
This is also a bad example, the file was originally over level and then was gained down to create headroom. This won’t work either as the files are already distorting.