Mastering—the final step in the music production cycle before manufacturing and distribution, and often referred to as the dark art of music production. While there’s nothing mystical about mastering, its mysterious reputation stems at least in part from a long standing confusion about it. Unsurprisingly, the most common question I get about mastering is, “What is that?” followed closely by, “How is that different than mixing?” Let’s shed some light on both of those questions.



If mixing were like an architect designing a house with many rooms, mastering would be like an interior designer sprucing up the rooms and tying the whole house together. If mixing were like creating a collection of paintings for a show, mastering would be like setting up the gallery space to have the optimal presentation of lighting, spacing, and location for the whole collection. If mixing were like a baker making cupcakes, mastering would be like setting up the window display so that each cupcake looks delicious but the whole collection looks like a masterpiece.



Put plainly, mixing is combining recordings of individual instruments to create a single piece of music. Mastering is combining individual pieces of music to create an album.



While I believe some of the confusion between mixing and mastering comes from the use of similar tools—equalization, compression, limiting, etc.—the responsibilities and mindset of a mastering engineer are indeed different.



The first job in mastering is to make each track on an album feel like it belongs with the rest of the album. One method of accomplishing this is with EQ. For example, a track with a dominant low frequency range followed by a track that is bright and aggressive could be jarring for the listener, and proper application of EQ could help correct both of these tracks, allowing them to sit together better. Equally important is adjusting the volume of each track to a proper loudness relative to the tracks around it. I’m not saying that every track needs to be the same loudness—quite the opposite, loud parts should be loud and quiet parts should be quiet—but the relationship in volume between tracks needs to be set appropriately. An entire album that is one constant volume tends to be boring; an album with too much separation between quiet and loud parts can be annoying for the listener who is forced to adjust the volume themselves or miss all of the quiet bits.



The second job in mastering is to make the album feel like it belongs in the context of other current albums in the same genre. Essentially, if you added the album to a playlist of albums in a similar style, would it fit? A pop album that averages 6 LUFS (Loudness Units relative to Full Scale) quieter than other pop albums would not fit. Likewise, a classical album that is heavily compressed also would not fit. It is common to draw comparisons with other albums in areas such as frequency balance, dynamic range, and loudness (though the pervasiveness of streaming normalization has had a small impact on that last one).



While the above jobs aren’t the only tasks that a mastering engineer does—other responsibilities might include attaching metadata to digital files, creating a DDP for CD manufacturing, preparing the audio for vinyl cutting, etc.—they are core to the role and mindset of mastering. Mastering is about seeing the big picture and closing the gap between having a collection of songs and having an album.

Input/Output is a Q&A column with mixing and mastering engineer James C. Hoffman. If you have questions about music mixing or mastering, you can write to James at inputoutput.gg@gmail.com. You can also find him on Twitter @JCHoffmanMusic.