What is Mastering? Understanding the Art of Music Mastering

In the early days of electronic recording studios, artists had to play and record their tracks live and in real-time with a single microphone and amp. Rather than being recorded step by step, the music was cut directly onto acetate. The introduction of analog magnetic tape technology changed the process, creating the profession of the 'mastering engineer.' Their job was to monitor the frequencies and levels of a recording, thereby keeping any needle jumps in check. Tape recordings were then transferred onto a template functioning as a master copy, thus enabling the large-scale production of vinyl records.

The role of a mastering engineer has constantly changed alongside the ongoing technological developments occurring in recording studios. When multi-track recordings were replaced by two-track master tapes, tools such as equalizers and limiters were introduced. These innovations allowed for improvements to the sound before the final cut, a technique that became increasingly popular during the pop music boom of the 1950s and 60s. It was during this era that the role of the mastering engineer, as we know it today, was truly established. The most skilled mastering engineers have played a pivotal role in the success of many records. For this reason, they were well compensated for their significant contributions.

Until the 1980s, the demand for talented mastering engineers continued to grow steadily. After the 1980s, advancements in digital technology began to reshape the industry. With the introduction of digital recording and editing software, many processes that once required a mastering engineer could now be handled with new tools and technologies. While this shift made mastering more accessible to independent artists and producers, skilled professionals remained essential for ensuring high-quality sound.

Today, despite the availability of advanced software, experienced audio mastering engineers are still highly sought after for their expertise in polishing recordings. At the same time, beginners on a budget often turn to AI mastering tools, which allow them to start publishing their tracks and build an audience.

Mastering is an essential step in the production process for several reasons, one of which is consistency. The artistry of mastering lies in the ability to create a balanced sound that meets a set of demands. Yet, achieving this consistency is challenging due to the wide range of playback options and devices, including hi-fi setups, headphones, radios, car systems, club sound systems, and portable devices. A track that sounds good in the studio may sound muddy in the car, requiring further adjustments. Thus, one essential task of a mastering engineer is to ensure that a release sounds good across all relevant mediums.

Consistency also involves maintaining uniformity across a project with multiple songs. For instance, when working on an album, the loudness of each track has to be considered in the context of the entire record, as the listener should not have to adjust the volume between tracks. Mastering engineers are also responsible for assembling the project by placing all tracks in the correct order and, if desired, ensuring they blend smoothly into one another. Consistent loudness, cohesive sound, and flow create a seamless listening experience throughout the project.

The second key task of a mastering engineer is to prepare the release for distribution. This step involves meeting industry standards and various technical requirements, including loudness normalization. Loudness normalization is crucial to ensure that tracks are neither overly compressed nor too quiet and adhere to the loudness standards of different distribution platforms.

One of the primary debates in mastering revolves around dynamics. This issue became prominent with the introduction of digital technology, leading to recordings becoming progressively louder due to the increased use of compressors and limiters. As a result, the natural dynamics of a song— the variations between louder and softer passages—began to suffer and become minimized. This effect is particularly noticeable on the radio, where dynamic processors and psychoacoustic effects further impact the sound.

Due to psychological reasons, louder recordings often sound subjectively 'better.' This situation ultimately resulted in the so-called "Loudness War,” which has faced criticism from mastering engineers advocating for a revival of dynamics in recordings. However, the importance of dynamics can vary significantly depending on the genre. Additionally, younger listeners have grown accustomed to a less dynamic sound. Streaming platforms have also contributed to this trend by normalizing specific loudness standards, thus shaping the current approach to mastering.

Another crucial element of mastering is file formatting, which is necessary to provide distributors with the correct files. Most distributors only accept high-quality options such as WAV or FLAC, which are also preferred by the majority of platforms for preserving audio fidelity. Moreover, the mastered files have to meet certain technical specifications, such as sample rate, bit depth, and file naming conventions.

Metadata embedding into the audio files includes track titles, artist names, album information, and ISRC codes. The latter are significant for tracking, reporting plays, sales, and collecting royalties. Although mastering engineers usually handle this task, artists can also verify and enter this information during the distribution process to ensure proper cataloging and display on streaming services and online stores. Lastly, final quality control involves thorough checks to identify and correct issues, such as distortion, clipping, or other errors.

During the mastering process, key elements to consider include well-balanced frequencies, a clear stereo image, mono compatibility, and dynamics. Ensuring well-balanced frequencies involves adjusting the tonal balance so that no particular frequency range consumes the recording. This is commonly achieved with equalizers and spectrum analyzers. A clear stereo image, painted with stereo wideners and imagers, helps maintain a sense of space. In contrast, mono compatibility ensures the track sounds good even when played on mono systems. In this context, phase meters help detect phase issues (i.e., a 'clash' of frequencies). Finally, engineers use compressors and limiters to manage dynamics, control the range between the loudest and softest parts of the track, prevent distortion, and achieve a cohesive, polished sound.

Modern mastering professionals usually have access to various hardware and software options to achieve all relevant goals. Hardware is valued for its precision and unique sonic characteristics. Key tools include equalizers, compressors and limiters. At times, analog tape machines and high-quality converters are used for adding warmth and maintaining audio fidelity.

Those working with software often strive to emulate the sound of analog equipment. Many software solutions come close to replicating the original sound at a much lower cost, contributing to the significant growth in mastering studios and a corresponding decline in prices. The rise of online mastering services in recent years reflects this trend.

Digital technology has prompted debates since becoming popular in the 70s. Analog fans sometimes criticize the lack of "warmth" and the low resolution of digital recordings, which was initially due to their relatively low bitrates (16Bit). The storm has died down a bit since then, and most studios now use a healthy mix of tried and tested analog equipment combined with the latest digital technology (which has been developed exceptionally well over the last few years). The best mastering studios possess an impressive arsenal of top-quality analog equipment and plug-ins. Getting the monitoring right is also very important: it is essential to use neutral and balanced speakers, and mastering studios often have several different loudspeaker systems to make good comparisons.