Mastering is often thought of as a mysterious art form and people have different definitions of what mastering is. Mastering in the simplest terms is the part of the recording project that provides a finished product for the consumer. There are two main goals in mastering. The first goal is to place a polish on the final mix so it sounds better overall. The second is to get the mix ready for consumer purchase. Just as a bad recording should not be fixed in the mix, mastering cannot cover for a bad mix.
There are engineers that specialize in mastering and that is all they do. The approach is a little different. In mixing the primary goal is to provide separation and to get a balance throughout the frequency spectrum. In mastering you look at the mix as a whole and work on gluing the whole thing together. You want to provide an overall balance.
The Tools Used in Mastering
Mastering Equalizers: are used to shape the tonal balance. Special equalizers are used for mastering. These EQs are called Linear Phase Equalizers. These EQs do not produce any phase distortion compared to regular EQs which in most cases produce a phase distortion algorithm
When mastering use broad changes with a wide Q. Using a couple of db to boost or cut will be more effective than surgical style EQ changes. Keep the volume at the same level. The reason for this is because our ears are more sensitive to the midrange and less sensitive to the low and high frequencies. Look into the Fletcher Munson Effect. If you adjust the volume lower than what you started off with then you may tend to reduce the mids in an effort to maintain balance. Mids are perceived as louder when listening at quieter levels.
Mastering Compressors: have different algorithms then compressors that are used in a single track. Their design and use is more of an effort to glue the mix together. Algorithms for compressors can include designs that are called FET Opto and Fairchild to name a few. A popular algorithm for mastering compressors is a design called VCA. There are mastering compressors built by a few different companies based on that algorithm design. A mastering compressor is a bit snappier. It reacts more smoothly and it reacts more quickly than some of the compressors used on tracks.
Multi-Band Compressors: may be required for adjusting the dynamics of specific frequencies or instruments.
Limiters and Expanders: are used to adjust the dynamics of a mix.
You can generally do more widening of higher bands without destroying the clarity of a mix. You may even want to try narrowing of lower bands to pull bass frequencies to the center of the mix. Keep checking mono compatibility with the stereo mix. You need to be careful of phase anomalies that can arise by widening the stereo image too much.
Harmonic Exciters: can add a slight edge to the mix. If one of your mastering goals is to add warmth, power, punch, and brightness then the Harmonic Exciter might be a good tool to use. Exciters are modeled on tubes, triodes and tape saturation. When tubes saturate, they exhibit a type of harmonic distortion that is generally described as warm.
Use with care! It’s very easy to overdo an exciter. This distortion creates additional harmonics that add presence or sparkle to the mix while still preserving a natural characteristic.
Brick Wall Limiters: can increase the overall level of the sound by limiting the peaks to prevent clipping and distortion. Then use the makeup gain to increase the overall loudness of the signal.
Dither: provides the ability to convert higher bit depths and sample rates (e.g. 24 or 32 bit 48k sample rate) to lower bit depths and sample rates. (e.g. 16 bit 44.1k for CD) While still maintaining dynamic range and minimizing quantization distortion. When you export a mix and you change the sample rate and bit depth, you will soon discover that the exported song will sound unnatural and kind of chopped up. It will sound unrecognizable. The problem is when you change sample rates and bit depths you are throwing away dynamic range and it becomes obvious in the export.
To get around this you apply dither with your export. Dither needs to be the last thing the signal goes through before the audio is exported. Dithering is the process of inserting a low level of noise. It needs to be applied anytime you change bit depth. There are different types of dither algorithms to choose from. The noise you insert is at a very low level but it will correct audio problems associated with changing bit depths. Dither only needs to be applied once and only during the mastering process.
Mastering with stems has only been around since the use of computers to record audio. Instead of just giving a mastering engineer a stereo track you break up the mix into more components known as stems. For example, you can give the mastering engineer the music and the vocals separately. This is so the vocals level can be left to the mastering engineer to adjust at the final stage. This process led to the final mix being broken up further for the mastering engineer. You can give the mastering engineer a whole mix with another version of the mix broken off into stems. Stems can be one stereo image of all the guitars together, or one stereo image of all the drums together. Well you get the idea. These stems combine to make the total mix.
The problem with this approach is the mastering engineer is now taking on more of a mixing role. This will cause the cost of the mastering to increase. Some mastering engineers don’t like to use stems because now their path of thinking has changed from a mastering approach to more of a mixing approach. On the positive side using stems may allow the mastering engineer an easier way to fix things they hear in the mix.
You can buy mastering plug-ins in group packages or sets. I use plug-ins from Sonar. My go to mastering plug-in is Izotope’s Ozone 5. It has a collection of mastering tools that are very powerful. The dithering algorithms are very good as well. All the tools mentioned in this article are included in this one plug-in. Blue Cat Audio is another company that makes really good plugins.
Mastering plugins tend to take up more system resources than plugins used in mixing. I highly recommend you keep the mixing process separate from the mastering process. Trust me when I say there are several good reasons the pros do it this way. If you are doing the mixing and the mastering yourself remember to apply dither at the very last stage. Only apply dither if you are changing sample rates and bit depths and only apply dither one time.