Audio Mastering Basics

No one will argue that digital technology has done much to empower musicians to take control over their recordings. Today’s artists are far less dependent on high-priced recording professionals, with many great-sounding projects having never even seen the inside of a recording studio.

But while the average modern laptop rig can run circles around the Abbey Roads of yesteryear, the knowledge and expertise of those old-school engineers has yet to be bundled into a plug-in. Some jobs are best left to the pros, and many would argue that mastering is one of them.

Certainly, if your budget allows, a professional mastering engineer is worth his or her weight in gold. While I’ll try to offer some basic suggestions on the process of mastering, bear in mind that it’s a skill that takes many years and special talent to master (no pun intended).

What Is It?

Mastering can be loosely defined as the fine-tuning of levels and equalization of a track, preparing it for replication and broadcast. This includes optimizing the average and peak volume levels of a track, using compression and equalization to achieve a level that’s consistent with other recordings.

Other chores a mastering engineer typically handles include cleaning up unwanted noises (clicks, pops, etc), arranging tracks into a final sequence, placing the proper amount of space between the tracks and inserting track markers and other codes required for replication.

More Than Meets the Ear

Technical explanations aside, trying to explain exactly what it is a good mastering engineer does is right up there with trying to define the process of a talented songwriter or producer. In the same way that anyone can lay down some loops and create a track, it’s not hard to plug in a mastering compressor and tweak a track’s parameters. But mastering and mastering well are two different things.

Mastering is truly an art form: a blend of technology, psychoacoustics, educated ears and musical intuition. In the right hands, the smallest increments of compression or equalization can have a major impact on the entire track. A good mastering engineer will make subtle decisions about sonic balance, bringing out the most important frequency ranges of different aspects of a recording and achieving a blend between the bass and high frequencies that can give a mundane track some punch and make a good track even better.

If you visit a mastering studio, you might be surprised by just how Spartan most of them are. Unlike major recording studios with their walls full of vintage gear and blinking LEDs, the best mastering engineers’ setups are relatively modest-looking affairs. Part of this is down to simple room acoustics: Those racks of gear on the walls can actually have a negative impact on the room’s acoustics and the ability to create a sonically neutral environment in which to monitor the mix.

Although their studios don’t boast rack upon rack of gear, the gear you do see is typically not a lot of off-the-shelf equipment. Most mastering engineers are partial to custom or highly-customized signal processing gear: discrete, class A electronics, vacuum tube circuitry, and other components closer to the rarified, top-end audiophile equipment than to professional audio processing gear.

Doing It Yourself

With the advent of high-end software and mastering plug-ins, more and more project studio owners are dipping their toes into the waters and experimenting with mastering their own works. The best mastering engineers have honed their craft over many years of practice, but if you’re realistic in your expectations you’ll probably find that a bit of experimentation will be a valuable learning experience. Even if you ultimately decide to go with a pro, you’ll be better prepared to know what to expect from them.

One of the first things to realize is that mastering is NOT mixing. While most mastering compressors can hone in on tight bands of frequencies, mastering does not deal with track levels, panning or other aspects of individual tracks in a mix.

So before you even consider the mastering phase, it’s important to put together a mix that’s as clean as possible. Keep everything in perspective, with good balance, panning, and no distortion. Use minimal compression on individual instruments, but even more importantly, don’t add compression to the final mix. The more you squash the mix, the less dynamic range you leave yourself for mastering.

One of the most common mistakes is creating a mix that doesn’t have enough headroom to allow for mastering. Less experienced mixers tend to try for as hot a level as possible, with peaks up to -1 dB or even 0 dB. But most mastering engineers will tell you that a minimum of 3 to 6 dB of available headroom is essential to performing good mastering. Ideally, your mix's peak levels should not exceed -3 dBFSD.

Once you’ve got a mix you’re happy with, it’s time to start experimenting with mastering. Your main tools will be dynamics processing (compression and limiting) and equalization. With both, a little is more than enough.

Avoiding the Squeeze

Probably one of the most important things to pay attention to in mastering is dynamic range. It’s also the most common mistake, and one that even more experienced mastering engineers sometimes get wrong.

Dynamic range is defined as the difference between the softest and loudest sounds in a recording. As compression is added to a track, the louder sounds are attenuated. As those louder sounds are squashed, the difference between the softest and loudest sounds—your dynamic range—decreases, and along with it all of your music’s the subtlety and nuance. The softest sounds have been brought up, and the loudest sounds have been limited, and the result is a track where everything is at its loudest, all the time.

Ask any veteran engineer what their biggest complaint about today’s radio fodder is, and they’ll all lament the disappearance of dynamic range. The past few years have seen an unfortunate trend toward pumping the overall level of music tracks higher and higher, adding more and more compression under the misguided assumption that louder is better. The problem is, eventually you run into those darned laws of physics.

With a mastering compressor, you generally want to start with a fairly subtle compression ratio. With a multiband unit like the UAD Precision Multiband Compressor, start with a ratio of around 2:1 and slowly (repeat: slowly) bring it up. Rarely, if ever, should you end up with a ratio of more than 5:1.

Equalization goes hand in hand with compression in mastering. A very precise multiband graphic equalizer like the UAD Precision EQ can compensate for changes in frequency balance caused by the application of compression. For example, adding compression might make the sound a bit muddy, in which case you’d use the EQ to cut a bit of lower midrange (around 300 Hz). Or maybe the compression has made the mix a bit dull sounding. Adding a tiny bit of high frequency EQ, around 12 kHz, can add some sheen and sparkle. A bit of cut at around 5 kHz might get rid of some of the harsh aspects of the drums and guitar parts. Of course, these are all just ballpark figures; your mix will dictate what needs to be done, and your ears should be the determining factor.

While you’re tweaking, it’s a good idea to compare your mix with a CD or two that sound good to your ears; preferably material that has a frequency balance and is somewhat musically close to what you’d like your tracks to sound like. This will help give you a point of reference, which is particularly useful after you’ve been making subtle changes for an hour or two.

Can you do your own mastering? You can try. Will it be as good as a real mastering engineer can do? Of course not. But spending some time listening critically to how these tools affect your mix is a great way to familiarize yourself with what mastering can do for your music. And the same way that adding too much reverb or EQ to an instrument is great for learning what not to do, experimenting with mastering plug-ins will go a long way toward educating your ears about what to expect from mastering, and how to tell a good mastering engineer from a not-so-good one. As always, it all comes down to using your ears.