Mastering monitors
Your audio monitors act as a magnifying glass and finetooth comb for picking out any errors and inconsistencies in your audio material, allowing you to correct it prior to duplication and commercial distribution. In a typical mastering house, the popular nearfield monitors we often find ourselves mixing on are nowhere to be seen.
In favour are the larger (and considerably more expensive) full-range main monitors, such as the Genelec 1035B (
www.genelec.com) or Quested HM212 (
www.quested.com), that offer unsurpassed levels of clarity,imaging, dynamics, and a frequency response that just isn't available to the smaller nearfield market. Often found soffit-mounted (flush to the wall), these monitors fire into a control room that's been acoustically optimised to minimise reflections, distortions, and resonances.
Of course, most of us can only dream of ever working in such a pristine environment, so you have to make the most out of your current monitoring set-up. Ideally you shouldn't be mastering on the same set of monitors that were used for mixing, otherwise rouge nasties may slip through the net without being noticed, so, at the very least, a secondary speaker system should be available, alongside your primary monitors.
Get to know how music sounds on a range of speakers, such as multimedia speakers or the popular Auratone Cubes (to emulate the typical television and small radio) and bigger hi-fi systems. If you're preparing music likely to be played in nightclub, be wary of over-hyping sub bass frequencies due to the inadequacies of your present monitors.
This is where a mate's megaWatt, stereo-on-wheels, car audio system could come in handy. The more references you have access to, the better. This helps you predict how your masters in progress will eventually translate on your intended audience's wide range of playback systems.
Next comes the room itself. Forget the speaker manufacturer's advertising blurb and technical specs for a moment; stop and listen to how the room sounds. Walk around and observe how sounds change throughout the room. These acoustic variations, caused by soundwaves collecting and reflecting, and rising and falling throughout the room, are perfectly natural phenomenons, yet can heavily influence the decisions you make during your track mastering. In my own studio, I discovered a mid-bass resonant peak after critically listening to numerous recordings I was familiar with. If I ignored it, I might have risked removing these frequencies during mixing or mastering through equalisation, so I rearranged my set-up by repositioning my workstation and monitors a little towards the centre of the room until I felt everything sounded more natural.
Are there any improvements you can make to your own monitor placement? Be aware of the room walls, floors, corners and ceilings that may be hyping bass frequencies, and note any hard surfaces that can reflect and smear mid and upper range frequencies. Sometimes it may be simply a matter of installing a set of heavy curtains over a window, or shifting a couple of racks of equipment. Most monitors are magnetically shielded to protect computer and TV screens from picture distortion, but also have a think about how your soundwaves may be bouncing off the sides of your computer monitor screen.
Mastering your meters
Mastering requires highly accurate level metering. The LED meters found on most mixing desks, as well as the displays in audio software, are generally set to track the fast travelling peak of the audio waveform with precision.
While this is essential for keeping a watchful eye on clipping when recording digitally by exceeding 0dBFS (FS = Full Scale, the maximum level a waveform may be encoded digitally), program peak metering does not relate too well to the real world. Our ears tend to respond to the slower, average volume level, while the ultra fast transients go unnoticed. Two songs with identical signal peaks may appear different in volume simply because one of the songs average level was lower. This is why analogue VU meters are still popular among studios because they give a good representation of how the human ear perceives volume.
Look for an RMS setting on your digital level meter, such as the PAZ Psychoacoustic Analyzer (
www.waves.com) plug-in for Mac to get a real world idea of the average volume. Most people strive for a loud mix, but be wary of setting your average level too high. Apart from becoming fatiguing to listen to, you may run into problems in radio broadcast situations where the station's limiters confuse the main energy of your track with the instantaneous peaks and attempt to squash it further. As a general rule, the difference between your peak levels and your average levels (known as the peak to average ratio) should never be less than 6dB.
One final point with metering: although it makes a terrific reference, a level meter is still not perfect. It registers evenly across the entire audio spectrum, whereas our hearing is more sensitive to mid-range frequencies, so always let your ears make the final verdict.
Another couple of worthy features from the PAZ plug-in are the Spectrum Analyzer, to visualise how energy levels are distributed among the audible frequencies (handy for comparing bass levels between different songs, for example); and the Stereo Position Display which also deciphers out-of-phase material. For a quick phase demonstration, reverse the polarity of the wires connected to just one of your stereo speakers (connect positive to negative, and negative to positive) and play back some music through them. Note the sensation of extreme width, minimal bass, and an obvious hole in the centre of the music. This is the due to the left and right channels working 180° out of phase from each other. The cones are literally pushing in different directions.
Sometimes, a sound can be thrown out of phase while recording or mixing if a channel is delayed for a stereo effect, or a studio cable or patchbay is wired incorrectly. Should the out-of-phase material be played through a single speaker set-up (like a television, for example), the true mono component of the audio would completely cancel out and become inaudible. So, be wary of out-of-phase sounds in the mix, and if in doubt, check it on a monaural source for compatibility.
Setting up
In order to get set up, the first step is to prepare your tracks for the session (see the Step-by-step #1 box on p113 for more on this). Close down all unnecessary computer applications so the CPU's clock cycles are available solely for music reproduction and accurate on-screen level metering. If you're accepting mastering jobs, ideally the tracks should be supplied on DAT or CD-ROM. Even portable hard disks are common these days. Audio on CD-R may be used, but is best avoided due to lost bits of data being unaccounted for during the ripping process when returning the CD back to a computer file.
Encourage your customers to supply their material without any main bus effects processing like compression or normalisation, and have them retain the same bit depth and sample rate that their mix was created in.
Every time a file is converted from a higher bit/sample rate down to 16-bit/44.1kHz (CD format), there is some degradation, either through truncating the extra bits from each word, or from the preferred approach of dithering. I personally mix in 24bit/44.1kHz and stay that way until the final stage of mastering when I'm ready to commit to dithering down to 16-bit.
Hearing is believing!
On a final note before delving into the actual process of mastering, you must consider the most important piece of test equipment in the studio: your ears. Every decision you make will be run past your ears for analysis, so there's a lot of responsibility riding on your ability to hear things as they really are.
Unfortunately, our quality of hearing fluctuates throughout the day, particularly after loud or extended listening periods, and when we're feeling tired and stressed, so always devote a fresh day to mastering. You may also wish to consider having your ears tested professionally, which would be a very good idea if you're setting out on a career in mastering.
Before starting a session, pop on a familiar (and professionally mastered) CD that compliments the style of music you plan to be working on. Don't monitor too loudly or you'll spoil your ears before you've even started! While listening, note the bass presence and definition; the prominence of the vocals, synths or guitars; and the detail of the cymbals and other treble in the mix. Observe your level meters: watch where the peaks of each beat sit, as well as the quieter periods of the piece. These practices serve to calibrate your hearing by placing a fresh reference in your mind of what things should sound like, in living colour!
Final advice
Maintain moderate listening levels. Once you think you've nailed a setting, turn it up to full room level and see if everything still sits right, before bringing your monitoring level right back down again to preserve your hearing's sensitivity. Always refer back to your reference material throughout the session to ensure you haven't steered off track into 'black & white' territory.
Listen for the message the composers are putting forth. They're ultimately the creative forces behind the music, and it's your role as the mastering engineer to enhance their original vision by working in harmony with it.
Although mastering is very much a technical process, the fundamental settlement of each mastering decision falls squarely back on your understanding and love for music as an artform. This appreciation continues to grow throughout our lifetime, allowing each of us us to broaden our proficiency at mastering through experience.