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Mastering Tips

What is mastering?

Mastering is the final step of a music production that adds a professional, commercial touch to your mixdown. In the mastering process, tracks are refined to sonic splendor and adjusted to industry standards. Once your tracks are mastered, they will sound balanced, clear and precious — on your kitchen radio, in the car, on the club PA and your headphones.

Mastering engineers typically work with a stereo mixdown provided by the producer or mixing engineer. Besides maximizing the audio quality, mastering also includes sequencing the tracks and preparing the pre-master used for replication and distribution.

In the 1990s, electro-mechanical processes were largely superseded by digital technology, with digital recordings stored on HDDs or Digital Tape and transferred to CD. The digital audio workstation (DAW) became common in many mastering facilities, allowing the off-line manipulation of recorded audio via a graphical user interface (GUI). Although many digital processing tools are common during mastering, it is also very common to use analog media and processing equipment for the mastering stage.

Just as in other areas of audio, the benefits and drawbacks of digital technology compared to analog technology is still a matter of debate. However, in the field of audio mastering, the debate is usually over the use of digital versus analog signal processing rather than the use of digital technology for storage of audio.

Although in reality there isn't such a thing as an "optimum mix level for mastering", the example on this picture to the right only suggests what mix levels are ideal for the studio engineer to render and for the mastering engineer to process. It's very important to allow enough headroom for the mastering engineer's work. Many mastering engineers working with digital equipment would agree that a minimum of 3 to 6 dB of available headroom is critical to perform good mastering. Ideal peak levels should not exceed -3dBFSD and the average sum of the left and right channels should be at around -10 to -18 dBFSD (As shown on the picture to the right).

There are mastering engineers who feel that digital technology, as of 2007, has not progressed enough in quality to supersede analog technology entirely. Many top mastering studios, including Bernie Grundman Mastering (which has mastered 37 Grammy-nominated albums), and Gateway Mastering still embrace analog signal processing (such as analog equalization) within the mastering process. Additionally, the latest advances in analog mastering technology include 120V signal rails for previously unavailable headroom of 150dB as well as frequency response ranging from 3 Hz to 300 kHz. In order to duplicate this frequency response in digital domain, a sampling rate of at least 600 kHz would be required, by the Nyquist–Shannon sampling theorem. However, it is pertinent that the extremes of these frequency ranges (3 Hz to 19 Hz and 21 kHz to 300 kHz) are effectively inaudible and fall outside the range of both human hearing and most professional microphones. 

The studio

The music mastering studio is very different from a normal audio recording studio. In fact, all the equipment and gear found in most recording and mixing studios can actually hinder the acoustics of a room to accurately monitor sound. Thus, the correct room acoustics and arrangement of the equipment inside a mastering studio is an important factor since the mastering engineer (ME) needs to hear in detail each mix. This room design should be non-environmental or with a minimum room interference. By working with an experienced mastering engineer, the recording artist is also open to more creative opinions and technical advice.

Process

The source material, ideally at the original resolution, is processed using equalization, compression, limiting, noise reduction and other processes. More tasks, such as editing, pre-gapping, leveling, fading in and out, noise reduction and other signal restoration and enhancement processes can be applied as part of the mastering stage. This step prepares the music for either digital or analog, e.g. vinyl, replication. The source material is put in the proper order, commonly referred to as assembly or (track) sequencing.

If the material is destined for vinyl release, additional processing, such as dynamic range reduction, frequency dependent stereo–to–mono fold-down and equalization, may be applied to compensate for the limitations of that medium. Finally, for compact disc release, Start of Track, End of Track, and Indexes are defined for disc navigation. Subsequently, it is rendered either to a physical medium, such as a CD-R or DVD-R, or to a DDP file set, the standard method of secure delivery for CD and DVD replication masters. The specific medium varies, depending on the intended release format of the final product. For digital audio releases, there is more than one possible master media, chosen based on replication factory requirements or record label security concerns. Regardless of what delivery method is chosen, the replicator will transfer the audio to a glass master that will generate metal stampers for replication.

The process of audio mastering varies depending on the specific needs of the audio to be processed. Mastering engineers need to examine the types of input media, the expectations of the source producer or recipient, the limitations of the end medium and process the subject accordingly. General rules of thumb can rarely be applied.

Steps of the process typically include but are not limited to the following:

Examples of possible actions taken during mastering:

Loudness

One of the most important steps in the mastering process is to enhance the loudness of a track. Loudness is the listeners’ individual perception of sound levels caused by an audio signal. In commercial productions, high volume levels are an important factor. Unprocessed songs are likely to be too quiet, which is disappointing if songs are published on radio or TV, where louder songs might attract more attention.

The loudness level is increased by using dynamic processors, such as (multiband) compressors and limiters, which reduce the dynamic range of an audio signal without affecting its dB level.

Limitations of mastering

One final word of advice — mastering cannot work magic. It adds depth, punch, clarity and volume to your mixdown. Mastering may hone the overall quality, but you’ll never get a poor mix to sound like a high end production. Here re-mixing the song will almost always lead to greater satisfaction.

Each step in a music production requires great care and accuracy — with this in mind, along with some experience, you will be able to achieve good results.