Audio mastering is a straight forward process when you understand its aims and the techniques involved in achieving those aims. The aims of mastering are simple: 1) bring a mix within a standard range of loudness. 2) Ensure clarity and tonal balance throughout a mix. 3) Add interest to important elements within a mix when appropriate. 4) Properly deal with track metadata and sequencing (including fade ins and outs). Some of these aims are not essential depending on what the client intends to do with the final track.

In order to achieve these goals standard techniques or processes are applied to a given track. Equalization, Compression, and Limiting are the most basic of these. Other processes are often used as well, but will not be discussed in this post. Here is a brief description of how to apply these three processes in a mastering setting:

EQ

Equalization can be used to add clarity, tonal balance, and interest to a mix. In the case of clarity, EQ can be used to pull out frequencies that stick out or interfere with the overall sound of a track. Say a tambourine masks part of a vocal sound and makes the vocal hard to understand. By reducing the frequencies on and around the tambourine one can add clarity to the vocal. In another example, say the reverb on the guitars and vocals are making the whole mix sound washed out. By using a high shelf one can pull the volume of the reverb down to add clarity to the mix.

EQ can also be used to change the overall tonal balance of a song. High pass filters can be used to suck out sub harmonic information that can shroud a mix and make it less punchy. A high shelf can be used to add or subtract from the information in the high end including the “air” around a vocal, the attack sounds of percussion and plucked or picked strings, and much more. A mid-range parametric EQ with a wide Q can be used to add presence to vocals and guitars, among others.

Finally, EQ can be used to create interest. Vocals are often the most prominent part of a mix and it is possible in mastering to process the mix in a way that will make the vocal stand out and shine slightly. One way to achieve this is to dip out some of the low-mids and pull out a few decibels between 1000 and 3000Hz. This leaves the presence or meet of the vocal and the S, P, B, and T sounds untouched. As a final touch and EQ can be used to add a very small amount of air to the top of the frequency spectrum to make the vocal sound as though the singer is right in front of you. This can be done with a vocal or any instrument to add interest to a mix.

It’s important to remember using an EQ to master a mastering engineer is not only affecting the targeted sound, but every sound at a given frequency. For this reason it is common to boost or reduce by small amounts; anywhere from 1-3 dB or less. Making a series of small changes, as apposed to larger ones adds up to create the desired balance and clarity. It should also be noted that EQ can be used in many more ways than described here. Through the use of mid-side processing a mastering engineer can be quite creative when sculpting the sound of a mix. (That being said, in my personal experience in mastering less is more.)

COMPRESSION

Compression can be used in the process of making a track louder, making a track clearer, and making a track more interesting. Compression does this by controlling the dynamic content of a mix. This can be useful when preparing a track to be made louder by pulling down leading transients giving theĀ  track a more consistent dynamic range. As a result the track will be hit less hard by a limiter or maximizer.

A compressor can also be used to make a track clearer and more interesting. One example of this is when wanting to make the drums more punchy. By using a compressor with a very short attack time (5-10 ms) and a medium decay time (100 ms) a mastering engineer can make the transients of the drums pop through the mix. This makes the drums not only more clear, but more interesting as well.

There are many reasons to compress a mix. In addition to wanting to control the dynamic in a general sense, or wanting to control the drum sound, one can also use a compressor to add presence to thin sounding guitars, control low end information, and more. Using a multiband compressor a mastering engineer can finely tune the ADSR (attack, decay, sustain, release) of individual bands and thus have dynamic control over specific parts of the mix.

LIMITING

In a mastering chain a limiter can be used similar to a compressor (a limiter is a kind of compressor after all), as described above, or it can be used in bringing the loudness of a mix to the desired level. By driving a signal into a limiter one can bring the dynamic level withing a certain range. When this is accomplished gain can be applied on the output to bring the track to the proper loudness (using a loudness meter).

There are attack and release parameters on many mastering compressors and limiters. These parameters can be used to add punch, presence, or glue a mix together. In a way, using these parameters is a way to adjust the overall tonal balance as well. Using a compressor or limiter in this way gives the engineer the ability to tailor a song’s sound to a genre specific tonal quality.

In summary EQ, compression, and limiting can be used in combination to raise the loudness level of a track, bring about clarity and balance, and add interest to a mix. These core aims of mastering can be accomplished by anyone who knows how to use these pieces of equipment, yet it is the professional engineer with years of experience who can craft quality masters consistently.

There is a science to and an art to quality audio mastering. These basic techniques are at the entrance of a trade that is both straight forward in approach, and complex in its specifics. Advanced mastering techniques will be discussed in a later post.