Very little in the field of audio engineering is more shrouded in mystery than the thing we call mastering. Does the name come from the idea of creating a master disc or from the stature of the master engineers that do such work? If mix engineer Bob Clearmountain is so good, why does he need mastering engineer Bob Ludwig to second-guess him before his work is mass-produced?
The proliferation of affordable mastering plug-ins, -programs, and -hardware devices has arguably replaced mystery with confusion. If I can create a viable Red Book CD, why do I need to spend money on mastering? If I own a Finalizer (see Fig. 1), can I offer my services as a mastering engineer?
This article will attempt to clear away the mystery and confusion by exploring the history and modern reality of mastering. We'll look at the craft's principles and techniques and discuss what an experienced mastering engineer brings to your project. We'll also discuss how best to use the services of a mastering engineer and what types of things you should consider when you want to go it alone.
WAY BACK WHEN
Back when musical performances were recorded directly to acetate masters, tracking, mixing, and mastering were done in a single step rather than independently as they now are. The role of the mastering engineer developed later, growing from the process of transferring tape recordings to acetate. Engineers who understood the complexities of the record groove could produce LPs that had a hotter overall level, more uniform tonal balance, and better signal-to-noise performance.
The role of the mastering engineer started with two essential functions: creating the physical master from which the product was mass-produced, and optimizing the audio for the sonic characteristics of the playback medium. In the early days of vinyl records, creating the physical master required very expensive and specialized gear. Therefore, mastering engineers were traditionally employed by record labels. Eventually, however, independent mastering houses sprang up, and that became the norm.
FIG. 1: The TC Electronics Finalizer is one of several products that encouraged mastering in home studios by bringing multiband compressions to the masses.
With the advent of the compact disc, a different manufacturing chain was required, but it would be more than a decade before average musicians had the capability of creating CDs on their own and sending them to be replicated. The mastering engineer continued to be the link between a finished mix and the manufacturing of discs. The process required digitizing analog content, formatting it according to the Red Book specification, and delivering it to the manufacturer, usually on Sony PCM-1630 digital tape.
In their sonic characteristics, CDs brought their own advantages and disadvantages, and mastering engineers adapted their tools and skills to optimize the sound. Seeing the power of talented mastering engineers to manipulate audio levels, for example, record labels began to push for louder and louder product in an effort to stand out from the competition on radio. For better or worse (see the sidebar “The Loudness War”), the role of the mastering engineer came to include making it loud.
Now that CD burners and Red Book — savvy software are abundant, why would anybody spend the time and money to have a project professionally mastered? There must be some reason, as virtually every major release bears an acknowledgment of the contributions of a mastering engineer.
Perhaps the most important function of a mastering engineer is providing independent judgment at the last stop in the line of audio-quality control. Unbiased and unaffected by peripheral concerns — like the producer's insistence on eight revisions of each mix or bickering between the lead guitarist and lead vocalist — the mastering engineer brings objectivity to the creative process. With fresh ears and an open mind, he or she can do much to shape the final outcome.
To that end, the mastering engineer prizes two tools above all others: experienced, trained, and sensitive ears, and an exceptionally accurate monitoring system. Whereas a mix engineer can (and must) focus on creating a unique and original sound, a mastering engineer sees every song in context with other projects in the same genre. The mastering engineer knows how to make a mix translate well on a broad range of playback systems, from boom box to home theater, as well as how to make it come off well on the radio.
In a mastering house, the acoustics and monitors are optimized for the most accurate and honest reproduction possible. Any glitches, clipping, or stray noises can be found and fixed in this pristine environment. Defects can easily be missed in surround mixes, making a quality-control pass even more important.
The mastering engineer is responsible for shaping a bunch of tracks into a cohesive album. If the project includes mixes created at different times in different facilities — even by different mix engineers — that can be a major challenge. How should the songs be ordered? How long should the gap between tracks be? Should engineer A's mixes be brighter or engineer B's darker to make them fit together?
TOOLS OF THE TRADE
The mastering engineer can't actually revise a finished mix, but by manipulating its tonal balance and dynamics he or she can make it smoother, edgier, or louder, or even change the relationships between different mix elements. Primary mastering tools include equalizers and compressor/expanders, but they are usually different than the units found in a mix room. A mix engineer will often turn to a “character” EQ or compressor, one that affects the sound in ways that go beyond the nominal settings. A mastering engineer, on the other hand, customarily uses the most neutral-sounding effects available. Such effects are ideal for surgical tweaks such as emphasizing a vocal that's too soft, but without affecting the rest of the mix.
Two special dynamics processors that have garnered much attention in recent years — both as weapons in the volume wars and enabling technologies for DIY mastering — are the limiter and the multiband compressor. The mastering engineer uses a limiter to reduce the highest peaks of a song so that its overall level can be boosted without clipping. For example, if a song has only periodic peaks above, say, -3 dBfs, those peaks can be reduced in volume, allowing the volume of the rest of the song to be increased by 3 dB. Multiband compression allows the manipulation of dynamics within multiple independent frequency bands. It can be a powerful tool in reining in the behavior of a kick drum and bass without adversely affecting vocals and guitars. (For more on multiband compression, see “Let's Split” in the January 2004 EM.)
Other processes may be required, depending on the needs of an individual project. A touch of additional reverb may help soften a mix. The stereo (or surround) image may require repair using middle-side processing or other specialized tools. (I have heard mastering engineer Bob Katz salvage a track by creating a believable stereo mix from a stellar live performance that was accidentally recorded in mono.) It's even appropriate in some cases to print an all-digital recording to analog tape for the warm, friendly distortion that only tape can provide.
If you intend to take your mixes to a mastering engineer, you can maximize the results and minimize unnecessary costs in several ways. For starters, communicate with your mastering engineer to be sure you understand each other. Let him or her know the nature and the extent of the project so that proper time is allotted.
Find out exactly what delivery media the facility can handle. In general, the less you do to the final mix the better. If you have mixed to analog tape, let the mastering house digitize the results from that tape. They have ultra-high-quality A/D converters just for that purpose. If you've been working in the digital domain, deliver your mixes at the highest bit depth and sampling rate your system can handle. When it's time for the final conversion to CD-quality files, the mastering house has the best tools with which to accomplish this task.
Files can usually be delivered on data CDs and DVDs, hard drives, or one of various data-tape formats (DLT, Exabyte, and so on). Any PCM file format (WAV, AIFF, or SDII) is likely to be viable, but under no circumstances should you send a version that has been subjected to lossy data reduction such as MP3, RealAudio, or Windows Media Audio. You can, however, save time and money by delivering materials that can be used directly without any format conversion or lengthy file-copying procedures. Audio CDs are less than optimal because of their 16-bit resolution and the time it takes to extract the audio. Again, communication is critical.
All materials should be documented thoroughly so that you won't have to waste time trying to remember which verse of a ballad needs fixing or which file has an alternate mix. It may be wise to come armed with alternative versions such as “vocal up” or “vocal down” to give the mastering engineer options.
Don't trim your files or tapes too tightly. A little breathing room at the top and tail of a song gives the mastering engineer more flexibility in creating appropriate gaps between tracks. You may also discover too late that you clipped a reverb tail, and although such an error can usually be repaired, it will cost you time and money.
GOING IT ALONE
FIG. 2: The L1 Maximizer plug-in from Waves is highly regarded for its ability to tame peaks transparently, allowing the overall gain of a track to be increased without affecting its perceived dynamic range.
Should you decide to master your own project, your best asset is time. Building in sufficient time helps you in two ways. First, it allows you to set your mixes aside long enough to gain some objectivity. Only by taking a few steps back can you be sure you're seeing the forest instead of obsessing over individual trees.
Second, extra time gives you the opportunity to listen to your mixes on a variety of playback systems. Checking your sound in the car, on a boom box, over big and small speakers, and with or without a subwoofer helps level the playing field between you and the mastering engineer who has 20 years' experience and a monitoring system worth tens of thousands of dollars.
Because one of your primary goals is to end up with a cohesive product, you should start by experimenting with the order and spacing of songs. That will give you a sense of the overall pace of the album — does the musical style and feeling flow sensibly from song to song? Once your songs are in a good order, consider how the songs compare sonically. Is one much brighter than the others? Is your ballad so loud that it fails to provide a respite between two driving songs?
Resist the urge to normalize all of your tracks. Normalizing raises the level of a track so that it peaks at 0 dBfs, and novices expect that this will put all their songs at the same level. Unfortunately, our ears don't perceive loudness based upon peak level — we make loudness judgments based on average level. To avoid clipping, you want the highest peak on the whole album to be a fraction below 0 dBfs, but the song-to-song balance needs to be determined by ear. If your software features RMS metering, that is more useful than peak metering for comparing loudness, but your ears are still your best tools.
If you want your songs to compare well to most commercial CDs, you'll want to be sure they're loud enough. The first step is to use a limiter to tame the highest peaks so you can raise the overall level. If you use a reasonably neutral-sounding limiter such as the Waves L1 Maximizer (see Fig. 2), this step will buy you additional volume without significantly affecting the sound or dynamics of your songs. Some engineers will instead search out peaks manually in the Waveform view, select the peak as tightly as possible, and process a gain reduction on just those few samples. Although time-consuming, this is a viable (and inexpensive) alternative to limiting.
After limiting, most commercial mixes are compressed, often quite severely. This is an aesthetic and pragmatic judgment — is it more important to preserve the dynamics of your mix or to “compete” with others' work? In making this judgment, though, be sure you are comparing apples to apples. Don't compare your mixes with what you hear on the radio, as radio engineers compress music even further for broadcast. Compare with the CD versions of songs in your genre, and let radio take it from there.
Try to maintain 24-bit resolution throughout the process, and dither when you bounce the mastered versions. Most good dithering software offers multiple noise-shaping options, so experiment with the different types to see which one is best for your music. Note that the differences lie purely in how noticeable the dither noise is in the context of your finished tracks.
Letting your ears be your guide is the primary point in mastering. The process — the songwriting, the performance, and the mix decisions — is mostly, if not purely, emotional, and objectivity is hard to come by. That is especially true for those of us who are songwriter, performer, and engineer all at once. Mastering sets aside the decisions, compromises, fatigue, joy, and angst that come with the creative process, and evaluates the sound of a project in its entirety.
For more information on mastering, I highly recommend The Mastering Engineer's Handbook by Bobby Owsinski and Mastering Audio by Bob Katz. You should also check out the article “Masters on Mastering” in the September 2003 EM and online at www.emusician.com for interviews with mastering legends Bob Ludwig, Stephen Marcussen, and Steve Hall.
Brian Smithersis a musician, engineer, and educator in Orlando, Florida.
THE LOUDNESS WAR
Much to the chagrin of many mastering engineers, there is a de facto competition among record labels to see who can have the loudest songs. It is an established truth that, all things being equal, humans associate “louder” with “better.” To the record labels, that means there's cash value in being louder than the song before or after on the radio or in a CD changer, and they push mastering engineers to make this happen.
There are two problems with this approach. First, severely reduced dynamic range fatigues our ears quickly. Musicians build their craft on notions of tension and release, and when a song is squashed so that the gentle moments are as loud as the intense moments, all that's left is tension. In the September 2003 issue of EM, mastering engineer Bob Ludwig expressed his frustration with this situation: “Never in the history of the human race have people been exposed to sounds as compressed as in the past few years.”
The other problem is that highly compressed CDs can actually sound worse over the radio because of the behavior of broadcast processors. How can they tailor the dynamic range of a song for broadcast if the song has virtually no dynamic range?
Because radio is not yet an issue for surround music, mastering engineers feel more freedom to retain dynamics in such projects. However, the ability of multidisc DVD players to shuffle between CD and DVD tracks may eventually lead to upward pressure on the loudness of DVDs.
To strike a blow for dynamic range, compare your mastering efforts to CDs, not to radio. Be sure to include some examples that are more than a couple of years old, before we reached current levels. Take your mixes to an experienced mastering engineer without having already mashed it with your bus compressor. Trust his or her judgment on the appropriate amount of compression to use.