Often misunderstood and overestimated, what is mastering exactly?
Audio mastering is the last step of an audio project before its release.

The purpose of mastering is to ensure that the mix will translate optimally on the different mediums, to quality check the project before its release.
It’s the place where you can eventually adjust subtly the audio content to the perfect balance, add some color if needed and optimize the release on all related systems and media formats. 

You can think of mastering as the last polish & quality check that optimizes playback quality on all devices (from little in-ears to high-end audiophile monitors or huge club’s sound systems).

Mastering helps to ensure listeners will hear the sound as the artist meant it.

The name comes from the idea of a master print. Which is then used to make all copies/duplications of the project. Copies, which are then distributed under multiple formats such as streaming, digital download, CD, Vinyl, Tape, etc.

Additionally, mastering is the place for the final quality check (QC) allowing to spot and fix the eventual clicks, pops, crackle or small issues that haven’t been addressed in the final mix (or earlier).

Mastering is also the place to ensure consistency and uniformity of sound over the multiple tracks of a project. Bring a cohesive feeling to it.

Why master?

The goal of mastering is to ensure that your audio will sound the best it can on all platforms. Music has never been consumed on more formats and devices than today.
One of the other main aspects of mastering is also to have your track reviewed by a fresh pair of ears, still objective on the project.  Who, if needed, will fix the issues or enhance it using high-grade tools carefully selected.

A good mastering job also makes an EP/Album consistent and balanced across all tracks. 

So what does mastering do?

Mastering is a complex process. Here are some of the techniques involved:

Fixing any small clicks, clips or other similar issues .

Ensuring a proper Stereo Image

Ensuring a proper Tonal balance

Ensuring a volume optimized & dynamics respectfull master with enhanced perceived loudness, definition in the hits, punch & tightness.

Ensuring optimization for digital release following the codec specifications of each platform.

Ensuring best Sample Rate/Bit depth for distribution using high quality Resampling & Dither if needed.

Ensuring Metadatas are properly inserted in the final files using appropriate tools.

Ensuring proper sequencing & spacing between multiple  tracks in a same project.

Make sure your project will be well received !