What does mastering a song mean?

Mastering a song is often a misunderstood concept in music production. To understand what mastering is, we should first understand the music production process.

Usually, the music production process starts with recording. In the past, that meant gathering in a large studio with the musicians, producers, and recording engineers to record the song together. However, nowadays most of the recording process happens in home studios or small project studios. Some genres don’t even require recording any real instrument at all. After recording every required part of a song, finishing all the little touches to the production like transition effects and such, editing all the instruments needed in time and pitch, the song is ready for the next stage: mixing. 

“So what does mixing a song even mean?” you can ask. That’s the stage when we, mixing engineers, gather all our power to balance the instruments in every way required for the style and the song.

I know it will be a bit confusing, but sometimes songs don’t even need us to balance them; they just need to be unbalanced so it makes sense. Does it make sense? Okay, let’s try this way.

What is needed for mastering a song?

Mixing engineers, or the person who mixes the song, use their knowledge of frequencies, dynamics, and depth to determine the instrument relationships and stylistic choices for which effects to apply to the vocals. These mixing decisions are often subtle, meaning they don’t push the song in a direction. Still, they help the song go into their directory easily and make the choices made in the recording and production process much bigger, usually. 

The song is a version of reality, but usually much fancier. For example, the drums you hear on rock records don’t really sound like that when you’re in the same room. Recording engineers and mixing engineers created that sound in studios.

Mastering happens when mixing is complete. When mixing is completed, the record sounds almost the same as you hear on the radio or your favorite streaming platform.

The number one job of mastering engineers is to double-check the choices made during mastering and to serve as the second pair of professional ears, providing feedback on the production. Often, artists, producers, and mixing engineers spend a handful of hours on a song before sending it to a mastering engineer; therefore, a pair of very experienced ears in a very controlled room with very expensive studio monitors, or even sometimes headphones, is invaluable. This is the last step in any music production process, fixing things before it's published. So, the responsibility of the mastering engineer is significant here.

The next purpose of the mastering process is to fine-tune the song's level, loudness, frequency, and balance. They don’t have enough data to balance the song as mixing engineers, but they do have some power to manipulate it. While mixing engineers work with all the separate instruments and channels in a song, mastering engineers work with only one file from the mixing engineer.

When a professional engineer masters the music, it sounds polished, complete, and finished. This doesn’t mean it won’t sound like that after the mixing stage, as mastering engineers are not witches and therefore cannot turn a bad mix into a Grammy-awarded master, but they can still polish what they have in their hands.

The process of mastering

The mastering engineers’ job requires them to be both objective and subjective. The process depends on the professional so the structure might differ between individuals.

Step 1: Objective assessment

The objective assessment of the mix starts by analyzing the song’s parameters to inform the mastering strategy, such as sample rate, bit depth, and file type. This is usually the first step because mixing engineers or producers sometimes send wrong or low-quality files. Assessing that everything is correct on that end is essential, as turning a low-quality file into a high-quality one is impossible. 

After ensuring everything is correct on that end, they analyse the song's decibel full scale (dBFS), level, and volume in the digital domain. Also, it’s impossible to turn back an audio file that’s already peaking above the digital limit (zero).

Some mastering engineers might analyse RMS and LUFS levels beforehand, but others do not.It depends on the person. Also, some measure the song all the time while working on it using meters, while others prefer to use their ears and check the meters only occasionally. That really depends on the style. Inspecting the waveform also gives a lot of information about the song and the mix, and it's easy to see if it’s too compressed or too dynamic with just a glance.

Step 2: Subjective assessment

Subjective assessment is all about the mastering engineer, and they often build that expertise over years of experience. It’s about the mix's audio fidelity and the listening experience. As if the song is pleasing to the ears, the genre is appropriate, or the mix is compelling enough for the song. They identify mixing issues such as improperly balanced frequency ranges, distortion, or non-musical artifacts.

They assess the Eleven Qualities of Superb Audio Fidelity, which include level, image, transients, depth, definition, clarity, detail, extension, dynamics, vocal halo, and blossom.

Step 3: The mastering process

After evaluating the song objectively and subjectively, the mastering engineer sets the roadmap and therefore decides which equipment to use and in what order. Mastering engineers sometimes work with digital audio plugins, sometimes with hardware units, and sometimes with hybrid systems. If their process requires hardware units, they handle the signal paths in this step before working on the song to ensure every unit works correctly and in the exact order they want.

They dial the mix gain first to bring it into their mastering chain. Mastering engineers often set target levels before working on the mix, so their equipment or mastering plugins work best. After that, depending on the song and the desired effect, they either work with equalizers or compressors. Equalizers (EQs) adjust the frequency balance of the song, from low to high frequencies. They cannot touch the individual instruments during the mastering stage, so they only work on the big picture. They also make adjustments to manage peaks, control dynamic range, or add apparent volume/loudness with compressors and limiters.

Essential tools mastering engineers use

Let’s discover the tools that a mastering engineer may need during the mastering process.

1. Equalization (EQ)

Mastering engineers use equalization to cut problematic frequencies and add frequencies they think the mix lacks, the genre requires, or simply to please the ears, such as very low and very high frequencies. If the necessary amount exceeds 2 or 3 dB, it often indicates a problem with the mix, so it might be better to go back to the source and fix it there.

2. Compression

There can be many different reasons for using compression in the mastering process. A mastering engineer can use them to control the transient peaks, manage the dynamic range, and increase the root mean square (RMS) level (loudness), and give the master punch and strength. Mastering engineers usually use very low ratios in this stage to keep the sound gentle.

3. Limiting

Limiters are essential in mastering to achieve high master levels without digital overs. They basically are compressors with an infinite ratio, so you can be sure that any signal is going over the threshold. They often determine the peak level. It might change depending on the genre, or some mastering engineers may have favorites such as -0.1, -0.2, or -0.3, or recently -1, to ensure there is enough headroom for the transition to bad codecs.

Advanced concepts in mastering: loudness and dynamics

Historically, mastering aims to make music as loud as possible without having artifacts to be competitive on platforms like the radio. However, this also comes at the cost of reduced dynamic range and transient detail, and they can distort the sound by hyper compression. Also, many music streaming services, such as Apple Music, Spotify, and Deezer, have built-in normalization features to keep listening levels consistent across songs and albums.

A song with more dynamic range will generally sound better than a louder one after normalization. This notion creates debates between mastering engineers and also makes confident stylistic choices. While some mastering engineers keep the music as loud as possible, others aim for greater dynamic range and make room for the listener.

Assembly and delivery

If the song is part of a collection (EP or Album), the mastered tracks are sequenced and spaced in the correct order. This includes setting the time between songs or creating cross-fades to achieve song-to-song cohesion in volume, impact, and frequency response. Also, mastering engineers are responsible for delivering the correct file formats and specifications. 

Standard formats include PMCD, Disc Description Protocol (DDP), WAV/AIFF files, and files explicitly prepared for vinyl or high-resolution distribution (such as Mastered for iTunes/Apple Digital Masters). Also, dither is used when rendering a high-resolution file to a lower bit depth (16-bit for CD) to reduce quantization error. The final critical verification of all aspects of the master before distribution is Quality Control. QC ensures the integrity of audio fidelity and the accuracy of release information and metadata (such as ISRC and CD Text).

Final words

In summary, mastering a song is all about making a more polished version of a good mix and getting it ready for all the different listening systems, from car speakers to earbuds, phone speakers to big PA systems in concerts. Their expertise and perfect listening environment help to achieve this, and they are always the second ear, even for a good mix prepared by another professional engineer.