Mastering Primer: Introduction Part 2
no image

July 25, 2007

 Article by finallymaster 

Welcome back to Mastering Primer…introduction Part 2. Last time, if you recall (or you can re-read part 1), I gave an introduction to mastering, as well as a basic itinerary of what I hope to cover in upcoming articles. Continuing on that theme, here is a brief overview of some of the basic tools and techniques required for mastering.


1. Mastering grade equalizers (analog or digital) Here are a few things that make mastering EQs different than any other EQ.

The sonic quality, dynamic range, signal to noise ratio and accuracy are vastly increased. Improved sonic quality, dynamic range, and signal to noise ratio are self explanatory. With regard to accuracy though, mastering grade EQs offer far more control over frequencies. Mastering EQs allow up to .5 to .1 db adjustments. We're talking surgical adjustments. In the studio you might be boosting or cutting big chunks of audio (anything from 2 to 15 decibels). In mastering we are refining, so the controls are click indented to assure repeatable settings, and accuracy to the above mentioned half to a tenth of a decibel.

Transparency. Here comes another seeming paradox. In mastering you want the EQ to be as transparent (unnoticeable) as possible. "What? I thought the purpose of EQ was to color and shape the sound??" Yes, but here's the clincher. General EQs, be they anything from studio/console/rackmount to stomp box style, not only affect the desired frequencies, but also add sonic artifacts of their own. Added harmonics (not always pleasant ones), and noise are the two main culprits. While those things might be unavoidable, and even desirable in tone shaping of guitars all the way to mix downs, during mastering we want NONE of that. Zip, zero, zilch. We want cut/boost, bandwidth, and frequency adjustment…that's it. No cool added distortion, no weird phase artifacts, and above all, no noise! Now that we got that out of the way, let's talk reality…no piece of equipment is totally transparent, or totally colorless. That defies the laws of nature. We refer to transparency in relative terms, compared to inferior equipment. We just want the most amount of transparency available. As a quick side note, a lot of equipment boasts great specs, like high dynamic range, low noise (signal to noise ratio) and wide frequency response, but what looks good on paper is not always the way things sound. A general EQ might share the same specs as a mastering EQ on the sheet, but that's where the similarities end. Hence, some of the chunky price tags of mastering grade EQs.

2. Mastering grade compressors (again, analog or digital)


All of what was said above about EQ applies to compression. That's simple enough. But here is a summary of what a compressor does, and how it plays its role in mastering.

Reduced to its lowest common denominator, a compressor simply raises the volume of low signals and lowers the volume of high signals. All of how much and when, is determined by controls called: threshold, ratio, attack, and release. Some more sophisticated compressors have more bells and whistles, but the main crux is those four mentioned controls. Threshold, controls the level your signal has to be at, for the compressor to start operating. Ratio, controls how much altering the compressor does…higher ratios have a much more dramatic effect. Attack, controls how fast the compressor latches on to your signal. Fast attack times clamp down on your sound quickly, while slower times allow some of the uncompressed sound to get through before clamping down, thus resulting in a fat, punchy sound. Release, controls when the signal returns to normal uncompressed status. With those controls you pretty much have complete control over an incoming signal. Now, most musicians use compressors as tools to increase sustain of their instruments. That's the #1 side effect of compression…the signal leveling and squeezing adds sustain…great for guitars, drums, vocals, etc. Usually, when used in that manner, compressors become a tone shaping tool. However, in mastering we are only interested in dynamics (volume control), not in added harmonics or sustain. So, we're back to our old friend, "transparency." Once again, think relatively, as anything you do, ultimately will make a difference tonally, no matter how insignificant!

Mastering compressors also come in single and multi band versions. Single band versions work on the whole signal fed into it, whereas multi band compressors chop up the signal into 3 or more sub parts based on user determined frequency points, and compress each frequency "band" individually. Both serve their purpose, and we will discuss the mastering engineer debate over the pros and cons of each at a later time.


3. This brings us to Limiters (analog or digital)

Once again, what was applied to EQs and compressors above, applies to limiters.

Limiters are similar to compressors in function and layout. Even the controls are the same, so I won't bore you with repetition. BUT…the main difference is that a limiter has one job only…to limit the incoming signal, and not allow it to get louder than a preset point. So, no matter how much signal or volume you apply, it will not go over the "limit". Also called a "ceiling".

That is how we prevent tape or digital overloads and when used in conjunction with a compressor, we can make the signal louder AND denser. With the compressor bringing up the rear, so to speak, and the limiter not letting the signal past a certain point, the ending result is a loud and dense signal. Now how much of that should be used, is a very hot debate going on right now which has spawned the "volume wars." A full article on this topic WILL be up in the future, covering the history of this war, as well as the scam that most of us have bought into. Anyway, back on track, compression and limiting are subjective topics, but good taste is paramount in not overdoing it, and ruining the original mix. Here is my rationalization for this. For argument sake, let's use a scale from 1 to 10. 1 being the lowest volume, 10 being the absolute max limit. So as an example, "Johnny smokin' aces Guitar" mixes his record and it looks something like this. Drums-8.8, bass-8.0, keyboards-5.5, guitars-7.7, guitar solos-100…just kidding- actually-8.7, vocals-8.5. He is really happy with the blend and mix. If we go in and start over compressing and limiting…that ratio might change from 8.8, 8.0, 5.5, 7.7, 8.7, 8.5, to, 9.0, 9.0, 8.5, 9.0, 9.0, 8.8, or something of that nature. You see we can easily screw up a mix, because things that weren't meant to be in the fore front, now suddenly are. The hard compression and limiting brought EVERYTHING closer to the ceiling max, AND also brought up the lower sounding parts (even though it was mixed that way on purpose!) to the same level. Dynamics and flow are gone, everything is thrown out of whack and we've ruined a good mix. That's an example of over doing it. But seeing how powerful these tools are, they CAN also be used to refine a rough mix, or tame a problem spot.

4. Noise control and reduction. This isn't the most exciting, but it is a necessary part of the cleanup. Here we use gates, expanders, noise reduction…all in single band and multi band format.

Gates, simply cut off a signal at a predetermined level. They are generally abrasive and blunt…great for special effects, or simply chopping off a section of noise with no music on it.

Expanders, work exactly like compressors, only in reverse. Once the signal hits a predetermined threshold, the expander kicks in, and simply shoves the noise far down, rendering it inaudible. This is a much more delicate and controllable form of noise control.

Lastly we have noise reduction units. They are not gates, they don't have the soul of a compressor….they simply analyze a signal, lock onto the noise frame (user adjustable of course) and remove it. Care must be taken though, in checking the original signal vs. the noise print signal, to make sure we aren't neutering any of the music. You would be surprised at how easily you can accidentally shave off a few KHz before you notice!

5. The last item I want to cover now is stereo image control.

These tools, on the simpler side, can widen or narrow a stereo sound, and on the complicated end of the spectrum, can manipulate ONLY certain frequency bands. The possibilities are endless. But care must be used again, because widening a stereo field too much (such as in getting a pseudo surround effect) can actually drop 3-4 db off of your signal. Conversely, narrowing the field can have the opposite effect, making all of your EQ, compression, and limiting calculations virtually useless. Again, proper compensation, and foresight are a requisite. By now I'm sure you've come to realize that the words "give and take" and "compromise" are a mastering engineer's mantra. We are still governed but the laws of nature…we can only bend things so far.

Once again, the purpose of imaging tools can be to correct an out of balance audio field, to enhance, and widen one, or to simply prep the recording for a particular market. An example would be, optimizing it for stereo compatibility, mono compatibility, or both, strictly for CD sales, fm radio, am radio, and so on. Of course, again, keep in mind, that for every method, there is a counter method, and for every counter method, there is a counter-counter method. The rabbit hole goes as deep as you WANT it to go!

P.S.  Aesthetic adjustments (fades, cross fades, song sequence etc.) as well as utilitarian functions (PQ codes, subtexts, plant protocol, etc.) are all performed on a DAW editing station. It is well advised to let the mastering engineer handle these tasks (to your specs of course). Leave all the heads and tails of songs uncut and unedited, as this will give the mastering engineer the proper room to edit and trim your pieces, as well as perform any of the aforementioned fades/cross fades.  More on this when we start discussing "prepping for mastering".

We'll stop here for now, as this will give you an idea of the basic steps involved in tuning a master. Technical comparisons and gear discussions will come later. As always, I'll do my best to keep the thread flowing logically from one topic to the next, but feel free to ask questions or make suggestions.


See you next time…

Back to Pro Audio Articles List