ABOUT MASTERING What it is, what gear to use, and what to listen to for...
Mastering audio material is a very specific discipline. As a matter of fact, it is so specific that there are dedicated mastering engineers out there who don't provide any other types of pro-audio services in their line of work. After having worked in the pro-audio field for the past twenty-five years, I can confirm that an experienced set of ears along with an exploration of the most modern trends in the audio industry play a big role in providing each client with high quality results. In addition, one needs mastering-specific tools in order to have the flexibility of tweaking client's mixes accordingly and since most clients these days mix their recordings on their own computers, the mastering engineer is expected to act as a jack of all trades in order to eliminate many mistakes and irregularities which often come out of this type of workflow - be it the mis-balance of individual instruments, an uneven overall frequency response, or the density of sound produced on average. The truth of the past remains still today - the better the mix, the easier the mastering of it.
INTRODUCTION TO MASTERING FUNDAMENTALS
Most mastering engineers of the past few decades have owned several high quality digital audio workstations with outstanding and reliable sound cards, pro-quality AD/DA converters, up/down-sampling decoders/encoders, and even digital external outboard gear collections in addition to the many types of internal plug-ins which substitute or replace physical equipment and are often bundled or purchased separately via online retailers such as Waves, Sony, McDSP, Digidesign, Avid, UA, and many more.
You may have also heard of loudness wars where newer releases seemed to have been louder than those issued before them simply because most humans perceive loudness with quality. It’s been proven that the louder someone’s perception of a recording is, the better it sounds when the two A/B tracks are compared with each other. It's a trick played by the nature on our hearing and takes a long time to get used to controlling. Fortunately, since the invention of iTunes and the iTunes Radio standard (among other online streaming services), new loudness measuring tools (such as LUFs meters) were introduced and because of them, mastering engineers no longer have to guess how loud their masters should be. This plain leveling field is very important as it gives us all a reference point to use when finalizing our masters.
For example, in May 2018 I ran a comparison of nearly twenty CD releases from various artists and labels ranging from acoustic jazz solo and combo releases, through folk and country recordings, rock and blues genres, as well pop music, such as Adele's 25. While most iTunes recordings have a recommendation in the range of negative 13-15 LUFs, some rock and pop CDs were -12 to -11 LUFs or louder, thus noticeably pushing the loudness threshold beyond reasonable limits. Subsequently, when these releases are then streamed online, they will sound smaller because the online algorithms will bring their levels down to negative 14 LUFs to match their streaming online standard. One can also see all transients present in these 16bit/44.1kHz CD rips and how they have been treated during the mastering stage. One can see how dynamic or compressed they are, limited softly or via hard knee and how they affect the overall sound and its peak levels. All these reverse sound engineering experiments I've been conducting for years have helped me get a more concise picture of where the music industry standards stand and how one's mixes and masters compare to the very best productions out there.
ANALOG OR DIGITAL MASTERING?
There is actually a straightforward answer to this question as explained in detail below. Know that this information is based on my personal experiences of working with both analog and digital concepts since the mid 1990s, so even though I feel confident that my recommendations below have a merit, it is also true that our knowledge and musical tastes keep expanding and changing as we grow older and more experienced and as new technologies and workflows are introduced by the recording industry players. Yet, it is possible to achieve outstanding results via various means and techniques as long as we let our experiences guide our ears accordingly.
1. When the original material is recorded using strictly analog means, such as analog mixing board, analog outboard effects and/or in addition is captured onto an analog reel-to-reel tape before converting and storing its digital copy fully inside the digital domain (projects involving reel-to-reel tape are rarer to see these days due to the cost of out-of-print tapes and time consuming maintenance/calibration of tape machines), my initial suggestion would be to stay entirely in the digital domain during the mastering stage. This is because the material recorded and mixed already features the warm sounding analog tube or solid state equipment along with the warmth and natural saturation of analog tape; therefore, the additional D/A and A/D conversion needed to use analog outboard gear for mastering tasks would diminish the final sound quality produced even when the best converters are used. So, in my experience, this is the time to use the very best digital outboard gear (where no conversion takes place) and/or plug-ins at the highest bit rate/sampling frequency possible (often delivered by the mixing engineer at 24bit resolution) and once finished with tweaking the overall sound, can be down-sampled and converted to 16bit/44.1kHz CD standard in the final stage.
2. When using primarily digital equipment to capture the sound of a recording in order to mix it at a later time via digital means (using DAW and its plug-ins or using digital outboard gear when available with A/D converters of some sort), this is where an analog master can make a huge difference and improve upon the original mix noticeably. Having worked with some of the very best digital and analog outboard gear myself built by legendary gurus of pro-audio inventions such the engineers of Neve, Teletronix, Tube-Tech, Neumann, Telefunken, GML, Calrec, Studer, Cadac, Universal Audio, SSL, Manley, Crane Song, and many more, I've learned to appreciate how their individual sound characteristics manage to color and enhance the often sterile-sounding digital tracks. Most solid state gear will use custom input and output hand-wound transformers known to color the sound of any audio signal in a positive way (while each unit does it differently, depending on the type), and most tube-based gear will provide the necessary warmth associated with acoustically-produced tracks of the past sixty+ years. Getting one's hands on working with as much analog equipment available as possible (thanks to used resale online stores such as eBay and Reverb) and using it on projects while mixing and mastering for clients is extremely beneficial to one's learning.
MASTERING TECHNIQUES AND THEIR CHALLENGES
Here are some simple rules I go by when mastering music, be it for clients or my own CD releases. One can always agree or disagree with my perspective. As has been mentioned, each one of us brings a different set of skills and tools to use, original experiences and ears to take advantage of. There are many different ways which can be utilized to achieve outstanding sounding results out there. Here is my take on it:
1. Have a consultation with each client, ideally before the mixing stage takes place, about what type of music, instrumentation, recording space, and mixing facility will be used before a final mix is delivered. Even the best mastering engineer can't substitute for a poorly produced mix, which lacks proper balance and dynamics. Soft mixes have a tendency to sound noisy when mastered to the industry levels, very hot mixes have a tendency to sound distorted, which is impossible to fix in post-production. It is ideal, if the client delivers mixes which are peaking around -3 to -4dBFs with some -25 to -21dBU RMS average loudness or -22LUFs. This gives a mastering engineer the proper amount of headroom to work with.
2. Consider stem-mixing. While most mixing houses may not be inclined to this request, stem-mixing gives each client much greater control over the final mix result, which can then be easily tweaked or recreated precisely using these individual stems. Stems are stereo files which feature pre-mixed individual instruments or groups of instruments already spread in the stereo field the same way they went into the final bus, including all effects imprinted in them. They are then blended with each other in the final mix bus during the summing process. Think of them as sub-groups on an analog mixer. This way, one can improve upon the overall balance of all instruments if some irregularities are discovered at a later time.
3. Mastering needs to provide a better sounding result than the original mix. If it doesn't, it is not done properly. When mastering, I'll often run the original mix on a separate stereo bus which I can go to at any given moment to A/B it in real time with what I'm working on while mastering. As mentioned, it is crucial that both A/B-ed stereo tracks have about the same loudness level, therefore I often lower the outgoing monitor volume of the mastering track in order to match the relative lower volume of the original mix. That way my ears are not fooled easily since louder always sounds better as already explained above. With really good mixes, one can apply EQ/Compression/Limiting to the entire album across the board. However, with uneven or unbalanced tracks/mixes one has to work on each song individually and therefore spend much more time tweaking and making it all sound leveled and balanced - something which the mixing engineer was supposed to do in the first place.
4. While most mastering can be applied to the entire Left/Right field spectra simultaneously, there are often instruments in the middle of the stereo field which need our help (most often bass, snare, and kick). Therefore, having the ability to use the Mid/Side mastering technique is of great help when one wants to tweak the center channel vs. both side channels. While there are quite a few plug-ins nowadays who serve this very purpose (Isotope's Ozone comes to mind), my all-time favorite still today is a master bundle by TC Electronics and their high end TC6000 hardware effects processor. This mastering suite has a very powerful MD4 engine, which provides me not only with M/S EQ section, but also a M/S compression section with up to five individual bands of compression to choose from.. The last chain of this bundle consists of a very high quality limiter, which offers quite a few options for limiting the peaks either in less or more aggressive ways. Its reverbs are also world-famous and to my ears still among the very best sounding out there. I use them often in my mixing sessions.
5. Once the high resolution master is completed, the one before the last stage of mastering is down-sampling to a CD format rates of 16bit/44.1kHz. This process too can be divided to either in-the-box experience (many software developers offer plug-ins which can down-sample high resolution files with a decent-to-high quality) or via digital outboard gear which often provides a higher audio quality experience but it is much more costly and time-consuming to work with as every transfer must be done in real time. My favorite hardware for this function is a combination of Prism Sound ADA-XR 24bit to 16bit reduction algorithms built into the unit itself (with four dithering curves to choose from) and the frequency and sample rate converter by Lavry aka DB Technologies known as 3000S.
6. Finally, when final master WAV tracks are finalized at 16/44.1, one needs to use a specialized software to print the final CD master onto a CD-R media before delivering it to a mastering facility. The master CD-R should include CD text and information about the owner, title, and lastly the ISRC codes (International Standard Recording Code) intended to protect the media and its creator. Sony's CD Architect (ideal for PC users) is still a good choice today since it also has the ability to provide a cue-sheet, although there are a few more modern programs available these days as well. For the past few years, especially with Covid restrictions in place, I’ve been using Hofa’s CD-Burn mastering software (for Mac) which allows master CD.DDP file distribution via online means.