Audio Mastering

Mastering is an art and a science. Mastering is the final creative and technical step prior to pressing a record album (CD, DVD, cassette, or other medium). Compare mastering to the editor's job of taking a raw manuscript and turning it into a book. The book editor must understand syntax, grammar, organization and writing style, as well as know the arcane techniques of binding, color separation, printing presses and the like. Likewise, the Mastering engineer marries the art of music with the science of sound.

The Craft of Mastering The audio mastering engineer is a specialist who spends his or her entire time perfecting the craft of mastering. Audio mastering is performed in a dedicated studio with quiet, calibrated acoustics, and set of wide-range monitors. Signal paths are kept to a minimum and often customized gear and specialized tools are used. The monitors should not be encumbered by the interfering acoustics of large recording consoles, racks or outboard gear. In other words, the acoustics are first optimized, and all other considerations must be secondary to the acoustics. For optimum results, mastering should not be performed in the same studio as the recording or with the same engineer who recorded the work. It is important to find a mastering engineer who will bring his expertise and unique perspective to an album project, to produce that final polish that distinguishes an ordinary recording from a work of art.

What is a Mastering Engineer?

The mastering engineer must have a musical as well as technical background, good ears, great equipment, and technical knowledge. Ideally, he should know how to read music, and have an excellent sense of pitch. He knows how to operate a range of specialized technical equipment, much of which is not found in the average recording studio. The successful mastering engineer understands many musical styles (and there are a lot out there!), edits music, and puts it all together with sophisticated digital processing tools. He is sensitive to the needs of the producer and the artist(s), and treats each project with individual attention. He must understand what will happen to the recording when it hits the radio, the car, the internet, or the home stereo system.

What's the Difference between a CDR and the Glass Master?

Premastering , not mastering , is the more accurate term, since the true master for a Compact Disc is called the Glass master , which is etched on a laser cutter at the pressing plant. In fact, the Glass Master is destroyed during the production process. The only thing permanent is the stamper, a round metal form that can be used to press thousands of CDs before it is replaced. There are two intermediate steps (the father and the mother ) before creating the stampers that press your CDs. If you're interested in learning more about the processes at the plant, visit So, we really should label the material that is going to the plant a PreMaster . The master for a compact disc must be in one of two forms: a DDP file, or an audio CDR (recordable CD). Both of which contain exactly the audio which is to be replicated as well as the PQ (track) data and possibly CD text or some graphics. Even though it's really a premaster, it's customary to label it a CD Master --because (hopefully) there will be no further alteration of the digital audio at any subsequent stages. If the pressing plant does its job right, the bits on the final CD will be identical to those on the master that left the Mastering House.

Why shouldn't I call my original file the "MASTER?"

The word Master is overused. I've searched record company libraries, and often found several tapes of a record album, each one labelled master, but in reality, there can be only one Master. You should label your tape or file Final Mix , or Original Session or Edited Work Parts , or Edited Compilation, Unlevelled or perhaps Assembled Submaster . But as you can see, using the label Master will only confuse things later on. Other confusions arise when the producer has second thoughts. He may decide to change the EQ or relevel a song, but forget to relabel the previous master. Certainly, the first thing is to prominently print DNU (Do Not Use) on the label of a newly obsolete tape.

Can't I just mix and put the file on the internet or CD? Seven reasons why you need mastering.

Every recording deserves good mastering. When you're through mixing, your work is not finished. Mastering adds polish, it sounds more than just a record...it becomes a work of art. The songs work together seamlessly, their sound can take on a dimensionality and life that enhances even the best mixes. Here are seven reasons why Mastering is needed.

1. Ear Fatigue
Most music today is produced by recording multiple tracks. The next step is the mixdown. This mixdown may take anywhere from 4 hours to 4 weeks, depending on the producer's predilections, the artist's whims, and the budget. Usually each tune is mixed in isolation. Rarely do you have the luxury to switch and compare the songs as you mix. Some mixes may be done at 2 o'clock in the morning, when ears are fatigued, and some at 12 noon, when ears are fresh. The result: Every mix sounds different, every tune has a different response curve.

2. The Skew of the Monitors
Monitoring speakers. It's amazing when you think about it, but very few studios have accurate monitor systems. Did you know, placing speakers on top of a console creates serious frequency response peaks and dips? A typical control room is so filled with equipment that there's no room to place a monitor system without causing comb-filtering due to acoustic reflections. And though your heart is filled with good intentions, how often do you have time to take your rough mixes around, playing them on systems ranging from boomboxes to cars to audiophile systems? Usually there is no time to see how your music will sound on various systems in different acoustic environments. The result: your mixes are compromised. Some frequencies stand out too much, and others too little.

3. More Me
The producer was supposed to be in charge. He tried to keep the artists out of the mix room. But something went out of control. The producer was gone for the day, or the bassist had a fit of megalomania. Or the artist decided to be his/her own producer. Whatever....all the mixes sound like vocal, or bass, or (fill in appropriate instrument) solos.

4. May I Have Your Order, Please
When mixing, you (the producer) often have no idea what order to put the tunes until after all the mixes are completed. If you physically compile these songs at unity gain, and listen to them one after another, it probably won't sound like "a record." Some tunes will jump out at you, others will be too weak; you may discover (belatedly) that some tunes are too bright or weak in the bass, or that the vocal is a little weak, or that the stereo separation is too narrow. These things actually happen, even after weeks in the studio, and the problems sometimes don't become apparent until the album is assembled in its intended order, or auditioned in a good monitoring environment.

5. The Perspective of another Trained Ear. The Buck Stops Here.
The Mastering engineer is the last ear on your music project. He can be an artistic, musical, and technical sounding board for your ideas. Take advantage of his special ear... many beautiful music projects have passed through his studio. You may ask him how he feels about the order of your songs, how they should be spaced, and whether there's anything special that can make them stand out. He'll listen closely to every aspect of your album and may provide suggestions if you're looking for them.

6. Midi Madness
Lately it sounds like everyone is using the same samples! Acoustic sounds are coming back in vogue, but perhaps you haven't got the budget to hire the London Symphony. So, you had to compromise by using some samples. But you shouldn't compromise on mastering. Good mastering can bring out the acoustic quality in your samples, increasing your chance of success in a crowded music field.

7. Don't Try This at Home
The invention of the Digital Audio Workstation (DAW) and the digital mixer is an apparent blessing but really a curse. Many musicians and studios have purchased low cost DAWs and digital mixers because they have been led to believe that sound quality will improve. Unfortunately, it's real easy to misuse this equipment. We've found many DAWs and digital mixers that deteriorate the sound of music, shrink the stereo image and soundstage, and distort the audio. There are several technical reasons for these problems-usually wordlength and jitter are compromised in these low-cost systems. Therefore, we recommend that you protect your audio from damage; use a mastering studio that employs a high-resolution system that enhances rather than deteriorates audio quality. Prepare your tapes properly, and avoid the digital pitfalls. Use the informative articles at the Digital Domain web site as resources to help you avoid audio degradation. When in doubt, take this advice: mix via analog console to a high-resolution file or to analog tape, and send the original tapes or files to the mastering house. You'll be glad you did. Those are only some of the reasons why, inevitably, further mastering work is needed to turn your songs into a master, including: adjusting the levels, spacing the tunes, fine-tuning the fadeouts and fadeins, removing noises, replacing musical mistakes by combining takes (common in direct-to-two track work), equalizing songs to make them brighter or darker, bringing out instruments that (in retrospect) did not seem to come out properly in the mix. Now, take a deep breath and welcome to the world of mastering.

Analog vs. Digital Processing in Mastering

Earlier in this article, I cautioned against returning to the analog domain once you've converted to digital. Ideally, you only want one of these conversions, once in the original recording, and once in the CD player playback.
But what about Pultecs, tube and solid state equalizers, tube and solid state compressors, limiters, exciters... Most mixing engineers can cite a plethora of famous processors that perform their work with analog circuitry. While useful for effects patching during a mixdown, a good number of these processors are unsuitable for mastering purposes. For example, an old, unmaintained Pultec may be a little noisy, but still be suitable to process a vocal or instrument during a mixdown. But would you pass your whole mix through that noisy box (maybe yes, if you like the sound!)? However, every processor used by a mastering studio (a good mastering studio) will be used in matched pairs, have calibrated positions, be quiet, clean, well-maintained. Calibrated positions are important for re-mastering, or for revisions. Clean means low-distortion and noise. Matched-pairs keeps the stereo image from deteriorating.

If a mastering engineer has a favorite analog EQ, or processor he wishes to use to create a particular sound, he should carefully balance out the cure versus the disease. There is always a loss in transparency when passing through analog stages, particularly A/D/A. Anyone who has patched processors in their consoles is aware of these tradeoffs. In other words, you have to carefully weigh the veil and fogginess that results from adding in an analog stage and additional converters with the subjective improvement from the processing versus processing the source in the digital domain. There will be an inevitable slight (or serious) veiling or loss of transparency due to each conversion. However, perhaps the mastering engineer feels the music will benefit from the sonic characteristics of a vintage compressor or equalizer...maybe he's looking for a "pumpy" quality that can't be obtained with any of today's digital processors (many people complain that digital processing is too "clean"...certainly a subject for another essay). There are many vintage "sounds" and other effects that still can only be obtained with analog processors. And finally, some mastering engineers claim that analog processors sound better than digital processors. I'm not one of them; I won't make that blanket statement. But I agree that analog processing is the "bees knees" for many musical productions. For example, I transferred a client's digital file to 1/2" analog tape and then back to 24-bit digital. Why? Because it sounded better. The analog tape stage did just the right thing to the source. I also had to make the fine choices of tape type, flux level, speed and equalization to help attain the spacious, warm, yet transparent sound quality my client and I were looking for. Ultimately, we used (and preferred) the analog dub to the original digital source for 8 out of the 10 tunes! Even without going through the analog tape, I have always maintained that A/D and D/A conversion processes are the most lossy part of the chain. When we do go back to the analog domain, I use the highest-quality D/A converter with low-jitter clocking, carefully calibrated levels, short analog signal paths and quality cables, and when converting back to digital, an extremely high-quality A/D converter. Then, the slight losses in transparency may be offset by the improvement due to the unique analog processing.

Our choice of whether to use analog or digital processing depends on the nature of the source, the music, and the tools we have on hand. I have some digital tools now which are so remarkable when used properly that clients with excellent ears cannot believe that the processing was not analog!

Unique Digital Processes

There are also some unique techniques that I cam perform only in the digital domain, one of which I call microdynamic enhancement , another is tonalization and the third is my patented K-Stereo Process (which is available to other mastering engineers).

For example, microdynamic enhancement can restore or simulate the liveliness and life of a great live recording. I've used it to get more of a big-band feel on a midi-sample-dominated jazz recording. I've used it to put life into an overly-compressed (or poorly-compressed) rock recording. It's really useful and extraordinary in helping to remove the veils introduced in multi-generation mixdowns, tape saturation and sound "shrinkage" that comes from using too many opamps in the signal path.

K-Stereo finds a use with unidimensional (flat-sounding) material, often the sad result of low-resolution recording and mixing. It is very different from the various width-altering processes that are now-available. K-Stereo captures and brings out the original ambience and definition in a source. The degree of stereoization is completely controllable. Instruments in the soundfield obtain a more natural space around them. The process is totally natural, utilizing psychoacoustic principles, and it's fully mono-compatible. For more information on this remarkable process, check out the K-Stereo.

DSP engineers are constantly inventing new ways to simulate all the traditional analog processes. So there's a lot to be said for digital processing, and I have no doubt that will become the dominant audio mastering method over time. For the forseeable future, in many cases we use a hybrid of analog and digital processing techniques to produce the best-sounding master.

Before Mastering: Mixing, Editing and Tape or File Preparation

Of course, before you get to the mastering stage, there is the mixing stage, which may be followed by an editing or processing stage. Many of you have purchased one of those new digital mixers to "stay in the digital domain" from beginning to end; many of you may have purchased a DAW (editing workstation) to prepare your tapes or files. Before Mixing: Please read my story, More Bits Please, which tells you how to use digital consoles and DAWs which mix, to their best advantage. Before editing or preparing your tapes for mastering , please read my article Preparing Tapes and Files for Mastering. You'll be glad you did.

Thanks for reading!