Introduction

The term mastering means the activity of making a master recording that can be used to manufacture (by replication or duplication) high-quality sales copies in a certain media or can be used for transmission over a certain media. The ''quality" of the master has to do with the sound quality of the sales copy.

Good mastering can make a poor-quality mix usable and "passable." Even though the mastering engineer does not usually have access to the multitrack master, different instruments can often be made louder and softer though careful equalization signal processing. The blend of the instruments and the "impact" of the instruments can be made better through dynamics signal processing (compression).

The Basic Mastering Process

The basic mastering process consists of compression and limiting that is done in several stages. Each stage of compression has a specific job to do for the sound and it would usually be a mistake to try and combine the steps. In-between the compression steps, equalization is applied to get the best frequency balance in the sound.
  
Before one begins to master, a reference CD typical of the kind of final sound you are seeking is chosen. This could be a hit in the style of your music or a band that has similar instrumentation. It is a CD you know sounds good in a variety of circumstances. You'll judge the quality of your master to this reference CD. Don't count on "remembering" the sound - use a reference CD.

Manual Level Corrections

Probably the first thing that a mastering engineer, mastering a "hit" single release (which would receive airplay) will do is make manual level adjustments to get a consistent loudness. Producers and radio program directors like tunes that "come on strong." This is often at odds with the way musical arrangements of tunes are done. For instance, many tunes start with a few instruments at the beginning and then every few bars another instrument is added. After a few "new" instruments are added in the introduction the level will noticeably come up. It sounds good musically, but it also makes the very beginning of the tune sound weak.

Equalization
It is best to use a seven-band or ten-band graphic equalizer, making your master have similar energy in each of the frequency bands, compared to the reference CD. When a compression step changes the frequency balance, you would use equalization to compensate for this tonal change. A step of compression may dull out the sound a bit, and you would compensate by adding treble frequencies (like energy in the 12,500 Hz range). If, on the other hand, a compression step made the sound more muddy, you would want to reduce energy in the upper-bass (around 320 Hz) or the bass-energy bands in general.

Compressing in "Stages"

In order to understand the compression used below, you need to be familiar with basic compression definitions and parameters. If you need to, study our companion reference article "Compression Parameters"

Stage 1: Adding Control Compression
The purpose of this compression stage is to control any sudden high-level peak that could cause the average level to be brought lower. This compression has much the same effect as "tape compression" in analog recording, and can be omitted if the mix was originally recorded on analog tape.
We need somewhat of a soft knee compressor will be used with a compression ratio moving towards limiting (5:1 to 9:1). Attack time should be fast (1 - 2 ms.) and the release time medium-fast (40 - 50 ms.). When we set the threshold so that gain reduction peaks to -3, so that it effects only the loudest peaks. Makeup gain can be set to restore level after compression (at least 2.0 dB). For mixes that have uncontrolled peaks, the higher ratios (8 or 9 to 1) should be used; slightly higher gain reduction could be allowed on these peaks, as long as there usually is no more than 3 dB reduction.
Stage 2: Adding Mild Compression
A mild amount of compression will give us general increase in apparent volume with very little objectionable effect on the dynamics of the tune. Done properly, the mix will often have twice the apparent level, especially in a mix that has a lot of musical dynamics.
When we say mild, we mean both a low compression ratio (between 1.5:1 and 2.0:1) and mild amount of gain reduction (6 dB). The attack time should be fast, but not at 0 (one or two milliseconds so that the compressor begins to compress right after any transient attack begins. We will be adding additional dynamics processing to control the initial peak of a transient, which is usually formed in the first 2 ms. The release time should be medium (100 ms. range) or a variable-release can be used.
We will be using a plug-in made by T.C. Electronic** called MasterX.** The compression and dynamic processing in this plug-in is done in three separate bands. The bass, midrange, and treble ranges are split, compressed separately, and re-combined back into one signal. With this kind of arrangement will prevent most compression pumping problems and make it much harder to hear the compressor working. .
The plug-in will automatically apply makeup gain after the gain reduction so that the original peak level is attained after compression. As you move the threshold slider down you will hear an increase in the volume of the lower-level passages and instruments, plus an increase in the apparent level of the mix.
Stage 3: Adding The Final Loud Edge
Final increases to the apparent level will occur by applying limiting to control transient peaks. We will often use a Waves** program called L1 Ultra-maximizer to accomplish this task. In previous compression stages we only controlled peaks after 2 ms. With the maximizer the attack time will set to "0" ms, and the release time at the ultra-fast setting of 1.0 ms. With these time parameter settings, the transient peaks will be literally sheared off. If you do not have a Waves Maximizer, use a fast-acting limiter and adjust the attack/release times according to the above times.
Care must be exercised in applying this limiting. Since it is literally clipping the signal, there is perceptible distortion being added. A little bit can cause a nice "edge" to the mix and too much causes it to sound dirty. The changing gain-reduction metering is fast-acting, making it hard to read the amount of gain reduction being applied. Fortunately, there is a maximum gain reduction figure (in dB ) that is displayed below the metering. It is a good idea to set the threshold for 5 dB or less gain reduction at this stage, although the ears should be your guide.

Don't expect to become an expert in one lesson.  Carefully following these guidelines, however, should greatly improve your final sound.