All About Mastering

Introduction

Mastering is the final creative stage of the music production process. It is the art of crafting a collection of tracks into an audio album, a CD production master, a vinyl lacquer, or a completed demo.

CD Mastering begins with the final mixes from the recording stage and ends with a CD Production Master tape, disc or file that is sent for pressing.

As mastering engineers we bring specialist skills and mastering equipment to this final stage.

Fresh ears can give a good perspective of an entire mastering project, when everybody else is so focused in on the detail that they have lost sight of the overall context.

We create balanced and accurate listening environments where we can hear, and compensate for, any anomalies in the recording process.

Mastering engineers are specialists. We don't claim to be experts at recording or mixing, because we have spent most of our careers mastering. For similar reasons, most recording engineers and producers prefer to pass their work on to a mastering engineer for the final stage.

The Listening Environment

The first thing a mastering engineer needs is a great sounding room.

In that room he will put some very good speakers.

Acoustic treatment and high-quality monitoring are crucial to a good audio mastering suite. With a balanced, accurate listening environment, it is possible to hear exactly how a recording sounds, and make judgments based on those observations.

Mastering engineers probably spend more time, energy, money, sweat and tears on acoustics and monitoring than on any other aspect of an audio mastering facility.

D to A & A to D converters

Most high-end mastering engineers like to use good analogue equipment for a lot of the sound processing that they do. High caliber Analogue to Digital and Digital to Analogue converters are therefore essential to ensure that the conversion between the analogue and digital domains is as accurate and real as possible.

Listening tests will prove that time and again that there can be a huge difference in quality between different converters, and so as mastering engineers we choose our converters very carefully and select only the best.

Compression

Applying compression when mastering reduces the dynamic range of the signal being processed. This involves making louder sounds quieter, and conversely, once you have applied a make-up gain, making quieter sounds louder.

Applying compression to an entire mix is very different to compressing individual instruments, as you might during the recording process. When mixing, for example, you might compress a lead vocal heavily to make sure that it is at a constant level and always cuts through the mix.

During the audio mastering process, however, we are applying a compressor to the whole mix: some sounds will be triggering the compressor, but all sounds will be affected by it.

Used clumsily, compression can flatten, distort, muddy and strangle your music.
Used judiciously, compression can add punch, clarity, drive and feeling to your music.

Equalisation

Usually called EQ, equalisation applies gain to a certain frequency while leaving others unchanged.

Mastering engineer’s use EQs to change the spectral balance of the music, in other words, to boost or cut various low, mid and high frequency ranges.

Mastering engineer’s use EQ for a number of effects when mastering:
To compensate for anomalies in the listening environment it was mixed in.
To bring clarity to vocals, guitars, snare, horns and other mid-range instruments.
To clear up a muddy bass, to add punch to a kick drum, to sparkle the cymbals.
To make all the tracks in the project sound balanced next to each other.

Once again, EQ used badly can destroy, EQ used judiciously can transform.

Level control

Leveling is one of the most powerful and often overlooked tools in a mastering engineer’s arsenal.

Setting the relative levels or volumes of each track is arguably the mastering engineer’s most important job. An album must have a level, or volume, and balance – with quieter songs sitting naturally alongside louder songs. An album should have dynamics too. An album should play through sounding even, without the need to adjust the volume.

The mastering engineer’s ears must be the final judge of the loudness of a track.
We will use different meters for reference, all with different meter ballistics and meter rules.
All these will help, but the final judgment must be that of our ears.
Never believe a digital tool that claims to ‘normalise’ tracks to the same level. Trust only your ears.

Limiting

A limiter is used to reduce the level of the highest peaks in an audio signal.

We use limiters to raise the perceived level of sound without creating over levels.
Once the mastering engineer has balanced the relative levels of your tracks, we will use a limiter to raise the loudness of the music to the optimum level.
Once again, delicacy is required to achieve the required level without causing distortion.
See the note ‘On Loudness’ for further discussion of levels and limiting in the mastering process.

PQing

This process is where the track start and end times are set for a CD Master. A CD player uses this information to skip to the start of any track. These start and end ‘indexes’ are called PQ points.

Often, these marks are obvious: when there is silence between tracks, there is a distinct start and end time for each track. In this example, PQ points can often be placed automatically.

Sometimes there are no gaps in the audio on an album, for example, a live album will have applause and audience noise; a concept album may have additional ambient material between tracks. In these cases, PQ points must be set at the most natural place for a track to start. In these cases also, the end point of one track will be the same as the start point for the next track.

Making the master

Once all the work is complete, we will then create the CD Production Master. This is what is used by the pressing plant to replicate the finished CDs.

The CD master is usually played off the mastering workstation in real time. This is the point where we listen through to check that the project plays well as a complete work.

A CD Production Master can come in many forms. These are the ones used by Mastering World.

Exabyte tape
This is an 8mm data tape, on which is stored a DDP image (Direct to Disc Protocol) and extra files with PQ information.
This is the format preferred by most factories.

CD Master data on a CD-ROM
Exactly the same DDP data as the Exabyte can be burned to a data CD on a computer's CD-ROM drive.
This is the most reliable way for us to deliver you a CD master online.
Download the DDP set of files, burn them to CD-ROM as data, and hand the disc to your replicator.

Let us know which factory will be pressing your CDs and we will transfer your CD master data to them.

Audio CD
Pressing plants and duplicators will also accept audio CDs for replicating, subject to conditions.
It must have been burnt as a disc-at-once session and must also have been finalised.

Having said all that, most of our clients request WAV files which they then burn to CD.

FTP direct to the factory
Again, this is the same DDP data, and it can be delivered online directly to the factory.

On Loudness

To keep up with demand for CDs to be louder, louder, and louder again, mastering engineers have been relying more and more on compressors and limiters to coax the loudest levels out of a given audio format. In the days of vinyl cutting, the pressure was to get the loudest ‘cut’ onto the vinyl master. These days, the same competition for loudness is happening to the CD format.

Any digital format has a finite limit to the loudness of a signal recorded onto it, defined by the number of bits - in the case of a CD, 16 bits per word. In order to make a CD sound louder, the music must be pushed closer and closer to that maximum level, using compressors and limiters. Before compression or limiting, a piece of music may have dynamics – quiet parts, medium parts, loud parts and very loud parts. The louder you want your CD mastering to be, the more you must take away from those dynamics. What is often left at the end of this process is all the elements of the music forced to be as loud as is possible. Whilst this can make a track sound punchy, hard and powerful, it can also make the music fatiguing to the human ear, which misses the variety of dynamics.

Of course, if loudness is the most important factor to you, a good mastering engineer will use all the tricks he knows to apply the maximum boost into your music. Please consider, however, the advantages of leaving some dynamic range in your finished CD masters. Your music will sound more natural, more expressive and more real.