What is Mastering...

 

You know that to capture good sound you have to have decent mics and preamps and a clean recording chain.  You know you have to mix your tracks in a way to make the project sound listenable and enjoyable.  Now lets go to the final stage, and it is here where you need to pay attention to mastering processors like those in the UAD-1 from universal audio, Waves bundles, and Izotope's Ozone, which is what I use.

Mastering, or finalizing, is the last stage of the process of making audio.  It is the final high resolution version of the production, the one from which you will spin off red book copies for cd and mp3 files for the internet.  When you have a great, not just a good, song you hear the advice to get it mastered professionally.  Dude, do it.  They have the gear, a specially treated room, and excellent monitors that most of us could not afford.   Plus it is always a good idea to have another set of ears that can listen to the piece more objectively. 

But for many of us who have yet to discover our magnum opus, we may want to try our own hand at it, to make the cd for friends sound better, or to make the demos we hand out sound great.  Or you may be a working towards becoming a sound designer, or building material for radio shows, or as an indie film composer who has to produces volumes of material so fast that mastering is out of the question.  Thanks to developments in plugin technology over the past few years, we can now turn our computers into home mastering labs.  While the result will not match that of an experienced mastering engineer with tens of thousands of dollars worth of hardware, with practice and a good ear you will be able to dramatically improve your production.
 

Getting Started

You may already be doing your own form of home mastering.  Are you adding compressors, EQs, and limiters after your mix?  Then you are. 

Develop 2 listening environments.  The first is obviously in your studio room where your computer is.  The second should be in a good sized comfortable room where the speakers are farther away, a living room, with its average home audio components, can work.   This gives you a reference outside your studio.  Speakers that are 8-10 feet away and interacting with the room will sound immensely different than those in your control room that are 4-5 feet away.  One goal is to get the audio sounding good on both.
 

Software file formats

Your mix should have ended with an uncompressed stereo file, ideally at high resolution, without any dither.  Use 24 bit depth, and if you can during the rendering of the mix, go to a 88.2 or 96 kHz sample rate (or higher if your gear and software supports it).  This lets you start with a high quality format which we will retain for the final master.   You might consider using the same software in some circumstances.  If you did the mix in Cubase, you could master there too.  Same for Logic and Sonar.  If you are going to use a different application, like Sound forge on the PC or Sound track pro or Peak on the Mac, just make sure the mix's file format is compatible.  No modern application should have trouble with a 24/96 .wav or .aif file.  

Most software will let you work in similar ways.  Essentially you have a mixer strip for the file and an output strip for the master out.  On the output strip is where your basic processors go, chained in a series in a definite order.

Note the meters from Logic illustrating the basic mastering setup.  I made this simple for the sake of illustrating the basic concept.  The file plays through its mixer channel without any processors here.  You could add them, but you risk overloading that channel, which you don't want to do.  The output channel strip is where the processors go, and they always end with a limiter of the "brick wall" type.  This kind of limiter will not let audio pass into the red no matter how hard it is pushed.  Indeed, this allows you to get your tracks up to commercial volume levels.

Loudness

Typically the loudness of the mix is nowhere near the top of the scale.  It may peake at .09, but its average level is well below.  Note how after going through plugins the audio is slamming against the ceiling at maybe 0.1, and if I wanted I could set the limiter to -0.05.  There is your loudness. If I stick that in my CD player I am as loud as any commercial cd.

Tonal Balance

But loudness is only one aspect to mastering audio.  Its the easy one.  Things get more complicated when we get into the tonal balance of the piece, which is effected by equalization or EQ.  Here you "shape" the mix into final form and can correct problems with it that might make it unlistenable  under some conditions.  It here where you need to put in hours of experimentation to learn to use this tool.  EQ at the mastering stage can drastically change the song's aural imprint.    They allow you to select the bands you wish to modify and raise and lower the volume of those bands.  The bands can be as narrow or as wide as you need them to be, from very wide gentle boosts or cuts to very narrow slices that are boosted or removed.

Buzzwords.  By boosting or cutting the bands on your equalizers, you can make your sound more or less "airy" (16khz), "bright" (3-10kHz) "harsh" (which is excessive brightness) "edgy" and "brittle" (2-6k) "sweet" (a slight but wide cut at 2-8k), "warm" (slight upper bass boost and slight 4k cut).  You can make your mix sound "thin" by reducing an wide band of frequencies from around 200-400 hz and make it "thick" by increasing those.  If you increase it too much you'll have a "muddy" mix.  Your bass can go from "missing" to "buried" to "solid", "fat", "boomy" depending on how you set the low frequency controls.

Can any EQ work?  To some extent yes, but overall, for best results, you need excellent plugin eqs.  Some software eqs are best for the tracking stage.  At the mastering stage they will make the sound worse. Mastering EQs are usually phase compensated.  Some may upsample the audio to high resolution, alter the sound, then downsample back to help prevent distortion and digital artifacts from creeping in. 
 

Compression

Compression is another tool the mastering engineer uses to bring out the flavor of audio.  Used effectively, compression can smooth out the piece.  It raises the volume of the softer sounds and reduces the level of the louder ones, to make them all more uniform to the ear.  Setting the attack and release of the compressor can yield a pleasing sense of dynamics that can set the whole mix in motion where all the instruments sound like they are on the beat and surging forward in the groove (even when they may not be).  The loudest element of the mix that the attack segment "captures" will trigger the subsequent gain reduction.  The decay will determine how long that reduction will last and the audio will rise again in volume till the next loud trigger comes through and starts the cycle all over gain.  Mastering engineers tend to love compressors as each has a different sonic imprint on material. 

Another type of compression used at the mastering phase is a multi-band compressor.  This is a processor that works to both tonally balance the piece by breaking up the audio bandwidth into 3 or more bands and having a separate compressor for each. 

The Order of Processors in the Plugin Chain

There is really only one rule.  The brickwall limiter has to be at the end to prevent any "overs" from occurring.  Otherwise the order is determined by your goals for the piece you are mastering. Mastering engineers earn their pay not just because they know how to set up the machines, but because of their experience in assessing the overall mix's strengths and weaknesses and then being able to develop a plan of attack to remove or reduce the weaknesses while maintaining or enhancing the mix's strengths.  You add a processor when there is a reason and need to do so.  You might not need to add eq if the mixdown engineer had the troublesome frequencies under control, or you might have to surgically remove an irritating frequency.  Rather than ask a question which has no absolute answer, why not experiment by changing the order in your plugin chain a few times.  How did it work when eq was put before compression?  Vice versa? Now you are gaining experience. 
 

The End of the Session

By using your ears and your knowledge of what each processor may provide, you begin to develop strategies for making the master shine.  The session ends when you have decided you have achieved this. Often that is a hard decision!  When is done, "done"!  Mastering audio is about listening and making decisions.  Its your ability to listen carefully, knowing what tool to apply and when, and a strong internal sense of what good sound is that leads to a successful session.  An interaction of ear and mind.  We all want good sound.  As you master your work, you have a shot a defining what that means, not only for others, but more importantly, for yourself.