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What Does a Mastering Engineer Do?

by | Mastering

Although this is the final stage of production and those without prior knowledge, it might appear a straightforward stage compared to recording and mixing; it is somewhat complicated and involves many more elements than one might expect. A mastering engineer (ME) has many responsibilities and is tasked with the obvious processing side of things, and they can enhance tracks and create an impact is just one of the things that make them sought after. They provide an essential service to the music industry. 

Using equipment in the forms of hardware and software, a practiced and informed ear, and technical savvy to make final tweaks to a track before it’s released, are some things that define what an ME does. So, what separates this practice from the rest of the production process, and why don’t mix engineers do it themselves (they have the capability)?

Most of the time, a mixing engineer won’t master their mixes because they’ve spent so much time developing the audio that they: 

a) might have a biased opinion on some issues.

b) miss specific things that need to be addressed. 

However, it is pervasive in the contemporary music landscape to be an independent artist who handles all elements of production themselves – the focus here is more on what a mastering engineer does (by trait). There will be plenty of valuable information for anybody in the aforementioned position and have to master their music. 

The most popular MEs have spent many years defining a specific sonic quality that they can assure clients, making them desirable against the rest of the market. As with anything in music, this is done by growing a network of clientele and building a reputation for oneself. The combination of having unique ears, equipment, listening environments, monitors, plugins, and processes (collectively) sets them apart from the rest.

Let’s break it down even further and take a look at some of the things we’ll be exploring in this topic: 

  • ME responsibilities
  • How do they do it?
  • Misconceptions

Each of these items has an array of sub-topics that will be broken down to establish the many angles of mastering and an engineer’s various roles. You might be surprised how much goes into this stage of production, and there could be some points to consider when doing it yourself or preparing your final mix for mastering.

The Responsibilities of a Mastering Engineer

There are some things that an ME is responsible for, and some of these things are, as you can imagine, somewhat complicated and require a fair amount of knowledge to undertake successfully. 

Below is a list of things we’ll be exploring to outline the responsibilities of an ME:

  • Final Stage of Production
  • Quality Control
  • Processing
  • Loudness
  • Correlate across multiple platforms and listening devices
  • ISRC Codes
  • Compilation of albums and EPs 

Final Stage of Production

In the vinyl realm, the role of the ME is to ensure that the final waveform of a track does not excite the turntable needle too much that it jumps out of the grooves. Since this is a physical process where the vinyl spins and the needle follows the grooves by sitting within them (the grooves correlate exactly to the waveform), it must sit comfortably for playback to be clear and unaffected. 

Nowadays, most music exists within the digital realm, which means there are fewer physical limitations to consider when mastering and a lot more freedom to experiment with how music can sound as a result.

The goal of any ME is similar – namely, to enhance the given audio’s loudness, clarity, impact, and feel by using their intellectual abilities and experience. 

Quality Control

This is the first thing that an ME will do, and it entails critically listening to the audio and checking a number of its features and parameters.

MEs will listen to the entire track and make notes on anything that stands out or may need addressing. If something doesn’t feel right, they will use some tools to establish what could be causing issues. Below is a list of things that act as methods of quality control:

  • The float size of your audio (16, 24, or 32 Bit) tells a lot to the ME. The larger the float, ideally a 32 Bit float, the more the ME has to work with. For instance, an almost clipping file will not be much of a problem if submitted on a 32 Bit Float, and headroom will be less of a worrying factor for you when mixing. 
  • Clipping – Your mix’s true peaks need to be below 0dB to avoid clipping and the undesirable effects that can come with it (such as distortion – the wrong kind). 
  • Phasing – these issues can generate strange-sounding audio because of the frequency cancellation resulting from mistiming and out-of-phase audio. This can make one feel uneasy when hearing it, diminishes the audio quality, and is undesirable. The mix will probably be sent back to you for revision. 
  • Down or Up-sampling  If your audio has been either down or up-sampled, traces of undesired artifacts could cause some issues. 
  • Distortion – This can be caused by some things and could very well be the desired sound, but in this case, it’s the bad distortion that will be looked out for. If it’s not meant to be there, this can ruin a track. 
  • Mono/Stereo – Some elements of a track need to be mono to avoid various issues such as phasing and to correlate across multiple listening devices without missing audio (yes, this can happen).


This is a lot more complicated than a matter of ‘dB’s. The ‘loudness wars’ have been underway for a while now and pose a constant battle to standardize the music’s perceived loudness. For example, a song played on the radio that sounds louder than the previous one will stand out more and grasp more people’s attention – this could increase the chances of sales. So for a while, people tried to make their music as loud as possible. 

However, nowadays, most of the online sites we use to share music have specific compression algorithms that can alter your music’s sound if it is too loud. This is where LUFS (Loudness Units Full Scale) becomes essential. This standard of measurement for audio considers human perception and electrical signal to determine its scale and differs from site to site. Some standards could be ‘-13 LUFS’ whereas others could be ‘-9 LUFS’.

MEs have to ensure that your track will translate well across the different algorithms to sound as good as possible anywhere it’s heard. 

Correlate across multiple platforms and listening devices

Music has become extremely accessible, which means that a lot of it is now listened to off phones, laptops, televisions, etc. Not everybody takes the time to enjoy it through a good sound system or cannot afford the luxury. This is where phasing and mono become important because that’s what most personal devices offer. 

A Hi-Fi system has stereo capabilities, meaning that panning and space will be easily perceived, but this is more difficult on the phone. If things are out-of-phase, their frequencies might be canceled out and become inaudible if played back through a mono monitoring system, and the track will not sound how it should. 

Another consideration is the frequency response difference across various devices. Phone speakers are not big enough to create low-end frequencies, but they still need to be noticeable to the listener, somehow. 

ISRC Codes

The International Standard Recording Code refers to the unique code assigned to your song to help with tracking of plays and remuneration of royalties. This is very important because it will be what determines you receiving an income from your work.  

MEs will do this for you.

Compilation of albums and EPs

Finally, an ME is responsible for compiling the piece of music – be it an album or EP – so that it flows well, is equal in volume, and ensures similar sonic characteristics across all tracks. Afterward, you should be presented with a final product that gels and sounds great. 

How Do They Do It?

Trained ear

This is not something that money can buy or any gear can help you with because a trained ear comes from years of practice. It is arguably, the most important tool of any mastering engineer because without a dexterous ear and the ability to determine what a track needs, you won’t consistently produce stellar work. 

You can become a critical listener and hyper-aware of the sonic frequency spectrum, but it will take time and repetition, as with anything. 

Processing (inboard and outboard)

Once the ME is happy that your files have passed the quality control and there are no significant concerns, they will begin processing the audio. Most of the mastering realm moves are slight and precise because their job is to enhance the given audio without changing it too much (unless that is wanted). 

EQ, Compression, Saturation, Stereo Imaging, and Limiting are all things that fit into the signal chain of an ME. Whether these processes are carried out using hardware or software depends on the engineer and their preferences. 

Unique processes (specific sound)

Each ME will have something that sets them apart, and with regards to the type of music at hand, there might be a specific outcome you’re looking for in the master. 

Depending on what gear, plugins, etc., are used in the process and how the differences will arise and set one engineer apart. 

High-quality monitoring system and listening environment (well-treated)

Equally important to having ‘well-trained ears’ is having a high-quality listening environment to work in. Some monitoring systems can cost upwards of $300 000 – if you’re looking at Kii Audio – and they are worth every penny, especially if you can use them well. This is not to say that you can’t do the job with a decent pair of studio monitors, but these systems are proven to be excellent and will be a defining factor in the sound produced by an ME. 

It is to be noted that without a well-designed, acoustically-treated room, the quality of your monitors is not essential, and you might not benefit from them as much. For good sound to be experienced, there needs to be an environment to facilitate it. 

For the most part, successful MEs have designed rooms that suit their needs, where they become very accustomed to the sonic character of that space, their speakers, and their gear, enabling them to produce music of such a high caliber. 


A mastering engineer cannot fix your mistakes. Therefore, you need to be sure of your mix before you send it off. They will use what they are given and do their job to sound as good as possible. 


A mastering engineer’s role is essential to the recorded music sector and the music industry as a whole. Since their conception, they have been at the final stage of production, acting as gate-keepers to quality and compiling records that have sufficiently impacted billions of lives due to their sonic characteristics and quality. 

Their influence on the record might not involve the most effort and time, but it has a severe impact on the final product, which is what they’re meant to do. 

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