Mastering is the process of taking a recording and enhancing it to its fullest potential. This not only makes each song from an album sound individually the best it can, but also makes the album as a whole sound unified. Also during mastering P&Q codes are placed on a recording for track markers, and timing information. This is how CD players know where each song begins and ends, and all aspects of time (remaining, total, elapsed).

One main area of mastering is equalization (EQ). In this aspect of mastering certain frequencies are augmented or diminished depending on the recording (often termed as "sweetening"). For example: By adding some high frequencies to a song, the overall effect could be a piece with more sparkle and energy. If a piece is sounding shrill then that piece may need suppression of some upper frequencies. Adding low frequencies could add more "umf." However, if the recording has a loud and flabby bass, then taking away some low end and adding some mid range frequencies will result in a tighter and more punchy and driving bass sound. The mid range frequencies {2k, 3k, 4k, 5k} are where the attack of the transient of a bass instrument such as kick drum is. By boosting these mid frequencies one can achieve a bass sound with good definition. If an instrument got buried somehow in the final recording mix, often that instrument can be brought out more by using EQ. Also if there are problem frequencies these can be notch-filtered out in mastering. For example: if there is a low 60 Hz hum that is on the recording that could be notch filtered out.

Not only must applied EQ make a certain piece sound good, but the entire album is taken into consideration. The album must flow from one piece to the next – even if the musical content is completely different.

The other main aspect of changing the sound of the music in mastering is known as compression. Compression is used to squash down (compress) the overall levels of the music. If compression is used correctly the average level of music can be raised without changing the quality of the original recording. Too much compression will take the life away from music (perhaps even adding breathing or pumping), while not enough compression will leave the music without any drive or punch, and sounding weak in comparison to other recordings. Compression can be used to color the sound if that is desired, but usually in mastering the goal is to make the music sound "better," not "different." Depending on the type of music and the recording, more or less compression will be used. A classical piece often will not have any compression on it while a heavy metal piece may need lots to keep a relatively high output throughout the music.

The optimal level for compact discs is 0db (the absolute highest level without digital overs). Usually the recording before mastering will have a lower peak level than 0 db. Optimizing is the process of raising the highest peak of a piece to 0 db. This is used in conjunction with above mentioned compression to achieve the loudest (often termed "hottest") level possible.

The editing phase can constitute many things. Often all that needs to be done in the editing phase is to place the songs in order and add silence between all the tracks. Depending on the original recording, a very short fade out to silence between tracks is often needed. This can usually be done without having to affect the music noticeably if at all. Also in the editing phase can be: fade-ins, fade-outs, cross-fades, cutting and pasting etc. (Example: If chorus one in a song is great, but the band ruined chorus two or three, the good chorus can be copied and then pasted over the bad chorus.) Editing can be done extremely precisely (down to 1/48,000 of a second).

Nine out of ten major mastering facilities use UV 22. The UV 22 Super CD encoding process developed by Apogee Electronics captures 20 bit resolution onto the 16 bit compact disc format.

P&Q codes are the track markers and timing information on a CD. These codes allow consumer CD players the ability to know where every track starts, ends, and all timing information about the CD (remaining, total, elapsed). The mastering engineer will carefully place these on the album.

Different facilities will give clients different formats for the finished master. Most mastering facilities are now using CDs as the final master (there are other formats such as 1630, DAT, and analog). The master CD should be a PMCD or a 1630 ready to have a glass master made from it at a duplication facility. As well as the CD, the mastering facility should give you a frame-accurate time log.

Most major mastering facilities have the ability to improve degraded recordings. Hiss, pops, crackle and other such undesirable artifacts can be removed from a recording depending on the severity of those sounds on the original recording.

This is a process in which the mastering engineer widens the stereo image of a recording.

Stereo imaging can also be used to help adjust the mix of some instruments. For example, by adjusting the stereo image a mastering engineer can bring the levels of instruments panned to center (such as a lead vocal) up or down.

A mastering engineer can remove unwanted sibilance (loud ‘S’ sounds). Harsh sibilance problems should be treated in the recording or mixing phase if possible.

Sometimes a recording will benefit greatly by adding just a little ambiance (reverb), such as with classical music that was recorded in a small room. The mastering engineer can add ambiance to make the recording sound as if it was in any type room – such as a concert hall in this case. NOTE: Usually the recording engineer or producer will have added any desired ambiance in the recording or mix down phase, so the mastering engineer will usually not add ambiance unless instructed to.

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