You've toiled with your final mixes for what seems like forever, and you're ready to commit the music to whatever its final delivery medium will be. Then

You've toiled with your final mixes for what seems like forever, and you're ready to commit the music to whatever its final delivery medium will be. Then a friend asks, “Who's going to master it?” You're stumped. A mastering engineer is supposed to take your precious final mixes and return them to you sounding even better and more professional, but what do these wizards really do behind the curtain?


Mastering can be a mysterious art, yet it is a critical step in audio production. Simply put, mastering is the process of taking a collection of recordings and optimizing them as a whole for delivery on a given medium, whether that's CD, vinyl, DVD, the Web, etc. Ideally, mastering makes the songs sound good on any system. Professional mastering studios offer optimum acoustic environments outfitted with top-shelf, ultra-flat monitoring systems. Mastering engineers often use a mixture of very expensive hardware, software or entirely proprietary systems to work their magic, yet by far, the most important ingredient in mastering is a great engineer's experience and trained ears. Mastering comprises numerous microsurgical procedures, including pop and hiss removal, overall level boosting and volume matching from song to song, precise equalization for bringing out the shimmer and punch of each track, and more. Although all mastering sessions do not require all of these procedures, the process typically involves at least three vital ingredients: equalization, normalization and compression/limiting.


Equalization is used to obtain a pleasing balance of frequencies (bass, mid, treble) in a mix, but it can also be used to eliminate unwanted hiss, clicks, pops or hum. Parametric or multiband EQs may effectively be used in mastering for any of these purposes. Multibands, while lacking the extreme surgical precision of true parametric EQs, often provide an easy solution for pulling out unwanted high-frequency hiss, low-frequency hum, small pops and glitches, or unnecessary sub-frequencies that muddy up the mix. Parametrics are often favored for their smoothness and precision in obtaining overall frequency balance. With a parametric, the engineer can boost or cut exact selected frequencies, along with as much or as little of the surrounding frequencies, as needed. An in-depth discussion of the nuts and bolts of equalization is beyond the scope of this article, but the November 2003 “Phantom Power” covered this topic. (Search for “EQ Opportunity” at

Normalization often follows EQ. It raises an audio file's overall amplification, while the file's dynamic range remains the same. Put another way, the entire audio file becomes louder, but the relative differences between the softest and loudest parts are unaffected. Normalization uses the loudest peak existent in an audio file as the basis by which it applies amplification up to a user-defined (or default) threshold or percentage. If two songs are equal in overall volume, but one song has particularly loud peaks compared to another, the one with the louder peaks will be less affected by normalization. This leads us to the third and arguably most vital (and misused) ingredient in the mastering process, compression/limiting.

Compression (which sometimes includes limiting, depending on the equipment) is the act of reducing the dynamic range of audio material while (typically) raising its overall volume. Limiting, basically, is the process of setting an amplitude threshold, beyond which a signal cannot pass. Why would you want to use compression instead of normalization if compression alters a finished song's dynamics? For one thing, compression and limiting frequently provide much finer control over the maximum volume ceiling, but more importantly, with compression the entire recording becomes audibly louder — and sounds punchier. This renders the finished material better suited for any delivery medium, especially radio. The mechanics of compression and limiting are complex subjects, but the “Phantom Power” columns in the March and April 2003 issues were dedicated to the fine art of compression. (Search for “Sonic Squeeze” and “More or Less” at


Because a mastering engineer will almost always apply EQ, often followed by normalization and/or compression, it is vitally important that your final mixes have adequate headroom. This means that, though you always want to record and mix with decently hot levels, it is often not a good idea to normalize your final mixes. Also, it is especially important (according to many mastering engineers) not to overcompress (or compress at all) your final stereo mixdown. Undoing normalization is a relatively simple matter of reducing the overall level of a mix by a few decibels. However, adding this other step can degrade the audio quality and be time-consuming (thereby, expensive). Overzealous compression, on the other hand, very often cannot be fixed at all. So, it is best to err on the conservative side with compression on final mixes, and I warn you against applying normalization or unnecessary level boosts; leave that up to the mastering engineer.

Mastering can enhance finished songs remarkably, giving them a coherent, polished sound and making your tracks stand out and compete in the professional pack. However, if attempted by an amateur, mastering can do more harm than good. It is absolutely a worthwhile, even essential investment. But remember, the most important thing is the engineer's experience and skill. Check out an engineer's samples and references. Make sure he or she is well-versed in your genre of music and try to attend the mastering session to provide real-time input. Done right, mastering can make the difference between low-budget sound and top-shelf results.