What are the main principles of audio equalization for mastering?

by Jesse Skeens

Equalization is used in both mixing and mastering but the two differ in how one approaches the task. With a mixing situation the engineer has control over each track individually which allows more control. In mastering usually only the stereo mix is available and this presents some issues.

When adjusting a stereo mix there is always a balance between fixing one thing and affecting another in a potentially adverse way. This is one of the skills needed to master, to enhance one area without hurting another. For instance if a vocal is not bright enough in a mix then the mastering engineer might add some high end to the mix. This might help the vocals but now there is a situation where the rest of the mix might be too bright. If the engineer carefully chooses frequencies that only affect the vocal and not the rest of the mix, for instance drums, then there might be a solution.

Another way around this would be to use an eq with an MS mode. This allows control of the frequencies on just the mono or stereo portions of the material. This way the vocal could be affected in the middle and anything on the stereo field would be left alone.

One of the main goals with equalization is to arrive at a tonal balance that is pleasing. This means from the low and all the way to the top end the balance of frequencies seems natural and musical according to the style of music. For instance a dance or rap track might need more top and bottom end to sound correct. A rock track might need more mid range to accent the guitars.

The music should also be clearly heard on a variety of sound systems from iPods to radios and night clubs. Every monitoring system will have it's own biases to the frequencies portrayed. So it is up to the mastering engineer to create a flat enough balance so that on average the mix sounds correct on all of these systems, when applicable.

There are two types of equalization, parametric and shelving. Parametric employs three controls, frequency, gain, and bandwidth. This is a good eq for surgical applications where specific points of the frequency spectrum can be focused on. The next type is shelving which generally control the high or low end of the spectrum. They are usually more gentle and can affect the overall tonal balance of the material.




This has been a basic rundown of how equalization is used in the mastering process. Although it is somewhat similar to mixing there are key points where it differs. Other components of mastering include compression and stereo control. All three constitute the basic methods for mastering a song.

Jesse Skeens runs a mastering studio located in London, UK.