While I cannot speak for all mixing and mastering engineers, there are some key differences in workflow between these disciplines, regardless of genre. Because mixers receive multiple tracks, a chunk of their job, at least in the earliest stage, is organizational in nature—labeling and color-coding tracks, ordering them hierarchically in a DAW, and creating instrument groups and submixes.
Once this is done, a mixer will proceed to more creative tasks like filtering, transient shaping, and effects automation that allow the separate tracks in a song to blend well together. Depending on how a production sounds when it reaches the mixer, a full song mix can take anywhere from a couple hours to days. This long time investment requires that mixing engineers develop a routine to maintain focus and avoid ear fatigue. Does it make sense to start with vocals? Or drums? Do you leave the tasks you enjoy least to the end or get them out of the way first?
Mastering engineers also need to be organized, but their focus is narrower. A typical mastering session goes something like this:
1. Critical listening: what does this song need to hit market and genre standards? Do I actually need to change anything? How should I order my signal path?
2. Set levels for the song based on genre, character, and release format.
3. Apply broad EQ and compression to improve tonal balance, while A/Bing the master with a gain matched original version for quality control.
4. Consider how the individual songs on an EP or album work together. Is the character and loudness of each song uniform and consistent?
5. Prepare export settings based on listening format. This might involve adjusting levels for conversion, resampling, and generating documentation.
The creative changes that happen during the mastering stage are subtler than those at the mixing stage (most EQ changes are around 1 dB up or down). But since they are made to a stereo file, there will be unexpected consequences that need to be listened for. Has a cut in the low-end somehow added edge in the presence range? Given how close a song is to completion once it reaches a mastering studio, the entire process rarely takes beyond an hour, so full album can be completed in a day.
Learn more about mastering workflow with The Mastering Workflow Webcast with iZotope Education Director Jonathan Wyner.
4. The room
To distinguish noises in a recording from something that is in the ambient environment, mastering engineers work in treated rooms that are quiet. You simply can’t hear the quietest detail in a song if there is a heater hum in the background, audible conversation in the room over, and traffic outside. And as the last person in the creative process before distribution and replication, a mastering engineer shouldn’t rely on guesswork.
While such a room is also beneficial to a mix engineer, they are typically more mobile than their mastering counterparts. Many mixers sideline as producers and find themselves moving from one studio to the next to work with artists on a project. To ensure a mix translates well across a range of playback environments, they will also switch between monitors, headphones, and even laptops to get a different perspective and suss out tonal balance issues.
This kind of jumping around doesn’t happen with mastering. To maintain a point of reference, engineers tend to stay put in one room they know well. A modern pop album can explore hip-hop, electronic, and sentimental ballads, with separate mixers handling each style. It would be a challenge to establish a sense of flow from one song to the next if a new setup was used every few hours.
Read Tips for Producing and Mixing in Headphones for more on the topic.
There is a lot of crossover in the tools used by mixing and mastering engineers, with a couple key exceptions. Let’s start the DAW. At the most basic level, mastering is about improving a mixed-down stereo file. Just about any DAW that hosts plug-ins and has good editing options is then appropriate for mastering. But depending on the format the music is going to be released on, as well as the distribution strategy, a mastering engineer will work with additional programs to create documentation about the master. Today, with the web as the most popular distribution channel, engineers submit a metadata container to streaming platforms that include artist name, song names, track duration, and more.
A second tool unique to mastering is a limiter, which is used to bring loudness levels to market standards—a song doesn’t have to be the loudest thing around, but it should be within the ballpark of similar music. Essentially a compressor with a 10:1 ratio, limiters are a safeguard placed at the end of a mastering chain to catch the loudest moments in a song as input gain in increased. This allows engineers to boost the quieter parts without pushing the highest peaks parts into distortion. Almost all songs benefit from some limiting, but given how aggressive it can be, often a little goes a long way.
To judge the overall level of a master, see the difference in the quietest and loudest parts of a song, and reference global loudness standards, engineers will rely on a metering plug-in, like Insight 2, which you can read more about here.
For those who are new to the world of audio, mixing and mastering can feel a lot less accessible than production or playing instruments. Hopefully the points listed in this article have allowed you get a better grasp of what happens behind the scenes during these important post production steps, so that perhaps you too will get in on the secret.
Learn more about mixing and mastering.