Mastering is the process that gives a finished mix its final polish, ensuring it sounds great on any device—from iPhone speakers to large club sound systems. It involves balancing the mix's sonic elements and optimizing them for consistent playback across all formats. This is achieved through precise techniques such as equalization, compression, limiting, and stereo enhancement. Essentially, mastering is what transforms a mix into a polished release ready for public listening.

The term "mastering" originates from the concept of creating a master copy, from which all other duplicates—whether streamed, on CDs, or vinyl—are produced. Mastering ensures optimal playback on all these mediums. Additionally, it maintains a consistent and cohesive sound across an album's tracks. Essentially, mastering is what prepares your audio for its ideal presentation upon release.

In 1948, the first true mastering engineers were born thanks to the advent of magnetic tape recording. Before this, there was no master copy as records were recorded directly to 10- and 12-inch vinyl.

In 1957, the stereo vinyl record came onto the market. Mastering engineers  developed techniques to make records louder. Loudness led to better radio playback and higher record sales. This marked the birth of the Loudness Wars that still go on today.

In 1982 the CD revolutionized mastering. CD masters required a different approach, although many of the analog tools stayed the same. That began to change in 1989 when the first digital audio workstations (DAW) with mastering software offered a mind-blowing alternative to the process.

Mastering is the last pass of quality control for your audio. If needed, hiccups in the original mix like clicks, pops and hisses can be addressed here. Small mistakes that stand out when the un-mastered audio gets amplified during the mastering process can be fixed as well.

Stereo enhancement helps develop the sense of space in your master. When done right, it widens your mix and helps it sound more enveloping. It can also help tighten your center image by focusing the low end.

Mastering compression manages the dynamics of the entire stereo track. 

It keeps louder signals in check while bringing up quieter parts to enhance the overall feel of the music. 

Compression helps glue the mix together and bring the right parts of the signal into focus.

The audio file type used during the production phase isn’t always the same as the final output medium. If the sample rate and bit depth need to be converted, it will be done at the end of the mastering process to preserve maximum audio quality.

If you’re planning to get digital distribution and publish your music this way, you may be wondering about mastering for streaming services.

It’s true that streaming takes a different approach to the overall loudness of the music you hear.

You might even have noticed that some tracks are quieter than others when you turn off volume match options in the app.

But it’s not only a subjective judgment. Audio measurement tools have shown that streaming services actually turn down the loudest material, leading some to conclude that the loudness wars have ended.

So what does that mean for your master? In some ways, it actually levels the playing field.

Now that engineers aren’t chasing the physical limit of a medium like CD, quieter, more dynamic masters don’t sound as lackluster by comparison.

In fact, a dynamic master may even sound more lively compared to flatter, more compressed tracks on streaming.

That said, dynamic range and loudness are a matter of preference for many artists and listeners. There are no strict rules about mastering levels for streaming services beyond getting a sound that works for your music. A little bit of variation may be less important than you think.

In the end, a great master by an experienced engineer or a sophisticated AI engine will sound good wherever listeners experience it.

Mastering begins by understanding the song's genre and style, as these dictate the sonic characteristics essential for the track.

The process of mastering a track may seem mostly technical, but it has its own sonic trends and fashions that come and go.

Depending on the genre—whether it's hard-hitting electronic music requiring loudness and punch, or jazz and folk needing a gentler approach—mastering adjusts for genre-specific requirements and expectations.

A traditional mastering engineer makes these decisions based on their interpretation of the song. But automated mastering can now do the same thanks to developments in AI technology.

The next step is to ensure consistency across all tracks of a release, creating a cohesive sound.

This involves fine-tuning the dynamics, frequency balance, and stereo imaging to match or complement each track within the album context.

Mastering engineers use their finely honed instincts to make these adjustments, aiming for a uniform listening experience.
This includes making subtle adjustments to each track to unify disparate elements and ensure that the album plays seamlessly from start to finish.

The final step of mastering is preparing the audio for distribution across various mediums—be it streaming, CD, or vinyl.

This includes final touches like sequencing the tracks, setting the spaces between tracks, and ensuring the audio meets the technical specifications of each format.
Special considerations might be necessary, for example, adjusting the bass frequencies for vinyl or ensuring the loudness standards are met for digital platforms.