Introduction to Mastering

It's not easy to do a great mastering job - but the sooner you start, the sooner you'll get better at it

by Craig Anderton

The art of mastering is the process of taking your mixes, adding any final polish (e.g., altering the tone, doing dynamics control, making sure levels are consistent, etc.) and in the case of an album, assembling the various cuts so they create a cohesive listening experience. You may even do things like shorten intros or solos, add reverb, or other more drastic changes—whatever it takes to produce a great-sounding recording.

However, the requirement for years of expertise hasn’t changed, and you still need good ears—and a serious skill set—to do mastering well. But the way to acquire years of expertise is to roll up your sleeves, start mastering, and learn the ins and outs of how the process works. If your mixes end up setting better after you’ve mastered them, you’re on your way.

We’ll get into specific mastering techniques in subsequent issues of the HC Confidential Newsletter, but before you even boot up your computer, it’s important to create a proper environment for mastering. Let’s look at what you need to think about as you get ready to start mastering.

THE IMPORTANCE OF YOUR ROOM

The single most important piece of gear for mastering is not a plug-in, rack processor, or software, but an acoustically-treated room. It doesn’t matter how good your speakers are, or what kind of a system you’re running, if you can’t accurately evaluate the sound because of room problems. Conversely, good room acoustics can show problems in other elements of the signal chain.

Acoustics is one of the main reasons why so many mixes that come out of project studios aren’t “transportable”: You mix something that sounds fine in your studio, but doesn’t anywhere else. That’s because you’ve mixed and then mastered to compensate for the deficiencies in your room, and other rooms will have different deficiencies. If you have an accurate response in your room, then the deviations won’t be as great when you play back your music in other rooms.

Acoustic treatment is a topic that could take up a book, and in fact, there’s a good one by Mitch Gallagher titled Acoustic Design For The Home Studio (Thomson Course Technology, ISBN-10: 159863285X, ISBN-13: 978-1598632859). While you can certainly improve matters yourself, if you have the budget, it’s worth calling a professional. When a friend and musical collaborator of mine, Spencer Brewer, was building a studio, he wisely allocated a significant portion of his budget to hiring a professional studio designer who was well-versed in acoustic treatment. Over the years, gear has come and gear has gone, but his fine-sounding room has remained the constant for all his work.

There are many sources of information on acoustics other than the above-mentioned book. Web sites for companies like Real Traps, Auralex, Primacoustic, and others often have a wealth of information and ideas on how best to tune a room. I do have a couple pieces of advice, though.

If you don’t have an acoustically-treated room and don’t think you need to do anything, for a real ear-opener set up an audio level meter (e.g., the kind made by Radio Shack for monitoring workplace noise levels; catalog numbers are 33-2055 and 33-4050). Sit with it in the middle of your room, run a sine wave test tone oscillator through the speakers, and watch the meter. Unless you have great monitors and an acoustically tuned room, that meter will fluctuate like a leaf in a tornado. Speakers by themselves do not have perfectly flat responses, but they look like a ruler compared to the average untreated room.

Fig. 2: Placing a speaker with its back against the wall often gives an apparent increase in bass; placing it in a corner accentuates the bass even more.

You don’t even need a level meter to conduct this test: Play a steady tone around 5 kHz or so, then move your head around. You’ll hear obvious volume fluctuations. (If you can’t hear the 5 kHz tone, then perhaps it’s time to look for a different line of work!)

These variations occur because as sound bounces around off walls, the reflections become part of the overall sound, creating cancellations and additions.

Another example of how acoustics affects sound is when you place a speaker against a wall, which seems to increase bass. Here’s why: Any sounds emanating from the rear of the speaker, or leaking from the front (bass frequencies are very non-directional), bounce off the wall. Because a bass note’s wavelength is so long, the reflection will tend to reinforce the main wave. This is a greatly simplified explanation, but it gets the principle across.

As the walls, floors, and ceilings all interact with speakers, it’s important that any speakers be placed symmetrically within a room. Otherwise, if (for example) one speaker is 3 feet from a wall and another 10 feet from a wall, any reflections will be wildly different and affect the response.

Some people try to compensate for room anomalies by inserting a graphic equalizer just before their power amp and “tune” the equalization to adjust for room anomalies. While this sounds good in theory, if you deviate at all from the “sweet spot” where the microphone was, the frequency response will be off. Also, heavily equalizing a poor acoustical space simply gives you a heavily equalized poor acoustical space. Like noise reduction, which works best on signals that don’t have a lot of noise, room tuning works best on rooms that don’t have serious response problems because you’ve already addressed any underlying problems.

THE MONITOR FACTOR

After the room (and your ears, of course), speakers are the most important element in mastering—again because you have to trust what you’re hearing. Traditional studios have large monitors mounted at a considerable distance (6 to 10 ft. or so) from the mixer, with the front flush to the wall, and an acoustically-treated control room to minimize response variations. The “sweet spot”—the place where room acoustics are most favorable—is designed to be where the engineer sits at the console.

In smaller, project studios, near-field monitors have become the standard way to monitor. With this technique, small speakers sit around 3 to 6 feet from the mixer’s ears, with the head and speakers forming a triangle.

Near field monitors reduce (but do not at all eliminate) the impact of room acoustics on the overall sound, as the speakers’ direct sound is far greater than the reflections coming off the room surfaces. As a side benefit, because of their proximity to your ears, near field monitors do not have to produce a lot of power. This also relaxes the requirements for the amps feeding them.

However, placement in the room is still an issue. If placed too close to the walls, there will be a bass build-up. High frequencies are not as affected because they are more directional. If the speakers are free-standing and placed away from the wall, back reflections from the speakers bouncing off the wall could cause cancellations and additions for the reasons mentioned earlier.

You’re pretty safe if the speakers are more than 6 ft. away from the wall in a fairly large listening space (this places the first frequency null point below the normally audible range), but not everyone has that much room. My solution, crude as it is, has been to mount the speakers a bit away from the wall on the same table holding the mixer, and pad the walls behind the speakers with as much sound-deadening material as possible.

Nor are room reflections the only problem; if placed on top of a console, reflections from the console itself can cause inaccuracies. To get around this, in my studio the near-fields fit to the side of the mixer, and are slightly elevated. This makes as direct a path as possible from speaker to eardrum.

ABOUT NEAR-FIELD MONITORS

There are lots of near-field monitors available, in a variety of sizes and at numerous price points. Most are two-way designs, with (typically) a 6” or 8” woofer and smaller tweeter. While a 3-way design that adds a separate midrange driver might seem like a good idea, adding another crossover and speaker can complicate matters. A well-designed two-way system will beat a so-so 3-way system.

There are two main monitor types, active and passive. Passive monitors consist of only the speakers and crossovers, and require outboard amplifiers. Active monitors incorporate any power amplification needed to drive the speakers from a line level signal. I generally prefer powered monitors because the engineers have (hopefully!) tweaked the power amp and speaker into a smooth, efficient team. Issues such as speaker cable resistance become moot, and protection can be built into the amp to prevent blowouts. Powered monitors are often bi-amped (e.g., a separate amp for the woofer and tweeter), which minimizes intermodulation distortion and allows for tailoring the crossover points and frequency response for the speakers being used.

However, there’s of course nothing wrong with hooking up passive monitors (which are less expensive than active equivalents) to your own amps. Just make sure your amp has adequate headroom. Any clipping that occurs in the amp generates lots of high-frequency harmonics (ask any guitarist who uses distortion), and sustained clipping can burn out tweeters.

One important point is that monitors have improved dramatically over the years, yet prices have spiraled downward; it’s now possible to get a truly fine set of speakers for well under a thousand dollars. If you’d like to do a little window shopping, here’s a good place to start and get an idea of what’s available.

IS THERE A “BEST” MONITOR?

On the net, you’ll see endless discussions on which near-fields are best. Although it’s a cliché that you should audition several speakers and choose the model you like best, I believe you can’t choose the perfect speaker, because such a thing doesn’t exist. Instead, you choose the one that’s as neutral and accurate as humanly possible. While some people advise that you choose a speaker that colors the sound the way you prefer, that’s the approach to take with the hi-fi speakers in your living room, not mastering tools.

Choosing a speaker is an art. I’ve been fortunate enough to hear my music over some hugely expensive, very-close-to-perfect systems in mastering labs and high-end studios, so I know exactly what it should sound like. My criterion for choosing a speaker is simple: Whatever makes my “test” CD sound the most like it did over the high-end speakers wins.

If you haven’t had the same kind of listening experiences, book 30 minutes or so at some really good studio and bring along one of your favorite CDs (you can probably get a price break because you’re not asking to use a lot of the facilities). Listen to the CD and get to know what it should sound like, then compare any speakers you audition to that standard. For example, if the piano on your mix sounds a little understated on the expensive speakers, choose speakers where the piano is equally understated.

One caution: if you’re A-B comparing a set of speakers and one set is slightly louder than the other (even a fraction of a dB can make a difference), you’ll likely choose the louder one as sounding better. Make sure the speaker levels are matched as closely as possible in order to make a valid comparison.

LEARNING YOUR SPEAKER AND ROOM

Ultimately, because your own listening situation is likely to be at least slightly imperfect, you need to “learn” your system’s response. For example, suppose you master something in your studio that sounds fine, but in a high-end studio with accurate monitoring, the sound is bass-heavy. That means your monitoring environment is shy on the bass, so you boosted the bass to compensate (this is a common problem in project studios with small rooms). When mastering in the future, you’ll know to mix the bass lighter than normal in order to have it come out okay.

Compare midrange and treble as well. If vocals jump out of your system but lay back in others, then your speakers might be “midrangey.” Again, compensate by mixing midrange-heavy parts back a little bit.

HEADPHONES, HI-FI SPEAKERS, AND SATELLITE SYSTEMS

Musicians on a budget often wonder about mixing over headphones, as $100 will buy you a great set of headphones, but not much in the way of speakers. Although mixing exclusively on headphones is not a good idea, I highly recommend keeping a good set of headphones around as a reality check (not the open-air type that sits on your ear, but the kind that totally surrounds your ear). Sometimes you can get a more accurate bass reading using headphones than you can with near-fields. Careful, though: It’s easy to blast your ears with headphones and not know it. Watch those volume levels (and be real careful about accidentally setting up a feedback loop—a loud enough squeal could cause permanent hearing damage).

As to hi-fi speakers, here’s a brief story. For almost 15 years, I mixed over a set of trusted bookshelf speakers in my home studio. These were some of the least sexy-sounding and most boring speakers in the world. But they were neutral and flat, and more importantly, I had “learned” them during the process of taking my mixes to many pro studios for tweaking or mastering. In fact, when listening over expensive speakers, the sound was almost always exactly what I expected, with one exception: Signals below about 50 Hz simply vanished on my speakers. Therefore, with instruments like orchestral kick drums, I had to mix visually by checking the meters, then verifying the mix at another facility. Thankfully, I’ve since upgraded to “real” monitors!

So while I don’t recommend it, you can use hi-fi speakers if you absolutely must, assuming they’re relatively flat and unbiased (watch out; some consumer-oriented speakers “hype” the high and low ends). However, they often aren’t meant to take a lot of power, so be careful not to blow them out. One other tip: Follow the manufacturer’s instructions about whether speakers should be mounted horizontally or vertically; it does make a difference.

Lately, “satellite” systems have appeared where the near-fields are physically very small—in fact, too small to produce adequate bass (some would argue that no 6” or 8” speaker can really produce adequate bass, but sometimes we need to reconcile finances and space with the laws of physics). To compensate, a third element, the “subwoofer,” adds a fairly large speaker, and is crossed over at a very low frequency so that it reproduces only bass notes. This speaker usually mounts on the floor, against a wall; in some respects placement isn’t too critical because bass frequencies are relatively non-directional.

Can you use satellite-based systems to make your computer audio sound great? Yes. If you’re living space is tight, is this a good way to make your hi-fi setup less intrusive? Yes. Would you mix your major label project over them? Well, I wouldn’t. Perhaps you could learn these systems over time as well, but I personally have difficulty with the disembodied bass when it comes to critical mixes.

TESTING ON MULTIPLE DELIVERY SYSTEMS

Finally, no matter how good your speakers and acoustics, before signing off on a mastering job run off a “proofing” CD or two and listen through anything you can—car stereo speakers, hi-fi bookshelf speakers, big-bucks studio speakers, boom boxes, headphones, etc. This gives an idea of how well the song will translate over a variety of systems. If all is well, great—mission accomplished. But if the CD sounds overly bright on, say, five out of eight systems, consider pulling back on the brightness just a bit.

Craig Anderton is Editor Emeritus of Harmony Central. He has played on, mixed, or produced over 20 major label releases (as well as mastered over a hundred tracks for various musicians), and written over a thousand articles for magazines like Guitar Player, Keyboard, Sound on Sound (UK), and Sound + Recording (Germany). He has also lectured on technology and the arts in 38 states, 10 countries, and three languages.