Your audience probably isn’t going to care about the little waver in the tenor part of your lead-off track, or that the cymbals are hard-panned L-R, instead of 75-75. What your listeners will care about is whether or not your music moves them, even if they don’t know why.

After pouring your heart and soul into the project, it’s common to develop “tunnel vision” and to have a difficult time seeing the forest for the sonic “trees”. You might obsess over something that most won’t even hear, while missing something that others will pick up on during their initial listen-through. If you’ve been working hard on your mixes for days, weeks, or months, you may well have hit a wall; your mixes sound very good, but you can’t make them sound any “better”. You’re not even sure if you need to keep trying.

Every listener has the potential to be affected by a different part of a mix, but there are certain aspects of a recording that have the potential to be more impactful or distracting than others. A professional mastering engineer has the ability to assess which elements of a recording should be highlighted or augmented (e.g. the vocal/solo, bass, drums, or depth/width) and which should be “fixed” or have less focus (e.g. sibilance, undefined low end, low energy, or “oomph”), and has both the tools and the ability to skillfully and musically make these adjustments.

Perhaps most importantly, a professional, independentmastering engineer brings an objective, experienced ear to the project, and won’t be influenced by non-musical factors such as egos, or decisions made during the mixing process which become so ingrained in an artist or mixer that they can lead to sonic “blind spots”.

2) You can’t hear everything that is happening in your mixes. More and more frequently, mixers are creating their music outside of the traditional recording studio. “Bedroom” studios are exploding in popularity as technology becomes more accessible and budgets continue to shrink. This allows for a great deal of creativity, and often yields some terrific results. But it can come at a cost.

Unless you’ve designed your home studio from the ground up with an ear towards negating nodes, early reflections, standing waves, and other sonic anomalies, it’s unlikely that you’ll be able to accurately hear everything that is happening in your room – and and in your mixes. This is especially true in the lower frequencies, which are extremely powerful and almost impossible to control with the usual acoustic treatments (foam, blankets, fiberglass, diffusors). As a result, at a minimum your mixes may have more or less low-frequency content than you think they do, and this can cause a number of issues both sonic (such as a “boomy” or “muddy” sound) and musical (fundamentals not ideally balanced).

Professional mastering rooms can accurately reproduce frequencies from ~20Hz to 20kHz, and are equipped with specialized and ultra-precise monitoring systems that will accurately play back these frequencies. In these environments a mastering engineer can quickly and reliably make decisions about a mix, knowing exactly how the music will sound in the “real world”.