When mastering music, it is common practice to allow the level to reach digital Full Scale on a sample by sample basis.
This can result in unwanted artifacts being added to the audio

The distortion is not harmonic, can be quite severe (more than 10 %) and cause early listening fatigue.

The key to remove this problem that we call 0 dBFS+ peaks, is to use a True-Peak Limiter like BRICKWALL HD.

The threshold can now be set safely at 0.0 dBFS, while BRICKWALL HD still takes care of peaks that would otherwise cause distortion.

The BRICKWALL HD limiter operates with highly-extended precision in both level (True Infinite headroom) and time (5 times oversampling).

Its processing engine, PPM level meters, History and Stats are all upsampled in order to identify intersample and 0 dBFS+ peaks in the precious Mix or Master track.

Therefore, the meter scales are extended to +3 dBFS because excessive level normally falls between 0 and +3 dBFS, and most consumer equipment already exhibits distortion at +0.5 dBFS.