Optimizing average and peak volume levels for proper relative loudness 
Signal processing - compression & EQ 
Arranging tracks in final sequence 
Timing of the space between tracks 
Establish a sonic "field" for all tracks 
Place track markers at head of all tracks 
Remove unwanted noise like clicks, pops, hiss 
Clean-up start and ending of each track (including fades) 
Insert Master Track Log – the PQ codes required for replication 

Loud and Proud.
Contrary to popular belief, mastering is only a little about making a hotter sound. While it's true that the gain, or 
volume level, is boosted during mastering, it may be that raw decibels are the least critical aspect of the process. 
What's important is the way mastering makes songs sound. "And today, "mastering can be loud as well as proud."

How Long Does it Take?
Although there is no limit to the time or money that can be spent on mastering, many people in the business state that a 
good rule of thumb would be an average of 8-12 hours for most albums, or in the neighborhood of an hour for each song. 
This assumes that the CD was well recorded and no additional processing requirements are specified. Additional time will be 
allocated depending on the condition of the original recording, a client's specifications and any unusual or custom needs

The Costs
Prices from respected mastering houses vary, but you can get excellent work for $120/hour. 
Of course, you can spend more, sometimes a lot more, but for the majority of artists, you can 
budget around "two dollars a minute" multiplied by "an hour per song" and be in the ballpark.

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History
 Pre-1940s In the earliest days of the recording industry, all phases of the recording and mastering process were entirely achieved by mechanical processes. Performers sang and/or played into a large acoustic horn and the master recording was created by the direct transfer of acoustic energy from the diaphragm of the recording horn to the mastering lathe, which was typically located in an adjoining room. The cutting head, driven by the energy transferred from the horn, inscribed a modulated groove into the surface of a rotating cylinder or disc. These masters were usually made from either a soft metal alloy or from wax; this gave rise to the colloquial term waxing, referring to the cutting of a record.

After the introduction of the microphone and electronic amplification in the mid-1920s, the mastering process became electro-mechanical, and electrically driven mastering lathes came into use for cutting master discs (the cylinder format by then having been superseded).

However, until the introduction of tape recording, master recordings were almost always cut direct-to-disc. Artists performed live in a specially designed studio and as the performance was underway, the signal was routed from the microphones via a mixing desk in the studio control room to the mastering lathe, where the disc was cut in real time.

Only a small minority of recordings were mastered using previously recorded material sourced from other discs.

[edit] AdvancesThe recording industry was revolutionized by the introduction of magnetic tape in the late 1940s, which enabled master discs to be cut separately in time and space from the actual recording process. Although tape and other technical advances dramatically improved audio quality of commercial recordings in the post-war years, the basic constraints of the electro-mechanical mastering process remained, and the inherent physical limitations of the main commercial recording media—the 78 rpm disc and the later 7-inch 45 rpm single and the 33-1/3 rpm LP record—meant that the audio quality, dynamic range, and running time of master discs were still limited compared to later media such as the compact disc.

Running times were constrained by the diameter of the disc and the density with which grooves could be inscribed on the surface without cutting into each other. Dynamic range was also limited by the fact that if the signal level coming from the master tape was too high, the highly sensitive cutting head might jump off the surface of the disc during the cutting process.

From the 1950s until the advent of digital recording in the late 1970s, the mastering process typically went through several stages. Once the studio recording on multi-track tape was complete, a final mix was prepared and dubbed down to the master tape, usually either a single-track mono or two-track stereo tape.

Prior to the cutting of the master disc, the master tape was often subjected to further electronic treatment by a specialist mastering engineer. After the advent of tape it was found that especially for pop recordings, master recordings could be made so that the resulting record would sound better. This was done by making fine adjustments to the amplitude of sound at different frequency bands (equalization) prior to the cutting of the master disc.

Record mastering became a highly prized and skilled craft, and it was widely recognized that good mastering could make or break a commercial pop recording. As a result, during the peak years of the pop music boom from the 1950s to the 1980s, the best mastering engineers were in high demand.

In large recording companies such as EMI, the mastering process was usually controlled by specialist staff technicians who were conservative in their work practices. These big companies were often reluctant to make changes to their recording and production processes—for example, EMI was very slow in taking up innovations in multi-track recording and they did not install 8-track recorders in their Abbey Road Studios until the late 1960s, more than a decade after the first commercial 8-track recorders were installed by American independent studios. As a result, by the time The Beatles were making their groundbreaking recordings in the mid-1960s, they often found themselves at odds with EMI's mastering engineers, who were unwilling to meet the group's demands to push the mastering process because it was feared that if levels were set too high it would cause the needle to jump out of the groove when the record was played by listeners.[citation needed]

 Digital technology 
Optimum Digital Levels with respect to the Full Digital Scale (dBFSD)In the 1990s, electro-mechanical processes were largely superseded by digital technology, with digital recordings stored on HDDs or Digital Tape and transferred to CD. The digital audio workstation (DAW) became common in many mastering facilities, allowing the off-line manipulation of recorded audio via a graphical user interface (GUI). Although many digital processing tools are common during mastering, it is also very common to use analog media and processing equipment for the mastering stage.[2]

Just as in other areas of audio, the benefits and drawbacks of digital technology compared to analog technology is still a matter of debate. However, in the field of audio mastering, the debate is usually over the use of digital versus analog signal processing rather than the use of digital technology for storage of audio.[2]

Although in reality there isn't such a thing as an "optimum mix level for mastering", the example on this picture below only suggests what mix levels are ideal for the studio engineer to render and for the mastering engineer to process.[3] It's very important to allow enough headroom for the mastering engineer's work. Many mastering engineers working with digital equipment would agree that a minimum of 3 to 6 dB of available headroom is critical to perform good mastering. Ideal peak levels should not exceed -3dBFSD and the average sum of the left and right channels should be at around -10 to -18 dBFSD (As shown on the picture below).

There are mastering engineers who feel that digital technology, as of 2007, has not progressed enough in quality to supersede analog technology entirely. Many top mastering studios, including Bernie Grundman Mastering (which mastered 37 Grammy-nominated albums in 2005 alone[4]), and some mastering studios still embrace analog signal processing (such as analog equalization) within the mastering process. Additionally, the latest advances in analog mastering technology include 120V signal rails for previously unavailable headroom of 150dB as well as frequency response ranging from 3 Hz to 300 kHz.[citation needed] In order to duplicate this frequency response in digital domain, a sampling rate of at least 600 kHz would be required, by the Nyquist–Shannon sampling theorem. However, it is pertinent that the extremes of these frequency ranges (3 Hz to 19 Hz and 21 kHz to 300 kHz) are effectively inaudible and fall outside the range of both human hearing and most professional microphones.

 The Studio
The source material, ideally at the original resolution, is processed using equalization, compression, limiting, noise reduction and other processes. More tasks, such as editing, pre-gapping, leveling, fading in and out, noise reduction and other signal restoration and enhancement processes can be applied as part of the mastering stage. This step prepares the music for either digital or analog, e.g. vinyl, replication. The source material is put in the proper order, commonly referred to as assembly or (track) sequencing.

If the material is destined for vinyl release, additional processing, such as dynamic range reduction, frequency dependent stereo–to–mono fold-down and equalization, may be applied to compensate for the limitations of that medium. Finally, for compact disc release, Start of Track, End of Track, and Indexes are defined for disc navigation. Subsequently, it is rendered either to a physical medium, such as a CD-R or DVD-R, or to a DDP file set, the standard method of secure delivery for CD and DVD replication masters. The specific medium varies, depending on the intended release format of the final product. For digital audio releases, there is more than one possible master media, chosen based on replication factory requirements or record label security concerns. Regardless of what delivery method is chosen, the replicator will transfer the audio to a glass master that will generate metal stampers for replication.
 

The Process
The process of audio mastering varies depending on the specific needs of the audio to be processed. 
Mastering engineers need to examine the types of input media, the expectations of the source producer or recipient, 
the limitations of the end medium and process the subject accordingly. 
General rules of thumb can rarely be applied.

Steps of the process typically include but are not limited to the following:

Transferring the recorded audio tracks into the Digital Audio Workstation (DAW) (optional). 
Sequence the separate songs or tracks (the spaces in between) as they will appear on the final release. 
Process or "sweeten" audio to maximize the sound quality for its particular medium (e.g. applying specific EQ for vinyl) 
Transfer the audio to the final master format (i.e., CD-ROM, half-inch reel tape, PCM 1630 U-matic tape, etc.). 
Examples of possible actions taken during mastering:

Editing minor flaws 
Applying noise reduction to eliminate clicks, dropouts, hum and hiss 
Adjusting stereo width 
Adding ambience 
Equalize audio across tracks 
Adjust volume 
Dynamic range expansion or compression 
Peak limit 

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Salvage Jobs
Sometimes, mastering engineers are called upon to do more of a salvage job than a simple enhancement.
Live recordings, for example, may need sophisticated EQ and dynamics, which is more than you can fit into the Final Effect slot.

The solution is use the D1600 more as a signal processor than a recording device. 
For example, run your two-track master into two inputs of the D1600, and use parametric EQ for the insert effect slot. 
Multiband limiting (DY3) might also be appropriate as an insert effect if the dynamics vary too much.

Next, for the Final Effect, insert dynamics processing to produce a smooth, hot-sounding master...then burn your CD. 
It's amazing how much some judicious processing can enhance material you thought might not be even useable.

Be aware, though, that mastering is a subtle process. A few dB or EQ or dynamics control is usually all you need. 
Higher amounts will unbalance the overall sound -- if you boost the bass a lot, for example, then the treble will sound thin by comparison. 
This is why mastering is considered such an art: it's all about subtle changes adding up to a major improvement in the sound.

There's no guarantee that using mastering tools is going to produce a great master recording, any more than 
buying a guitar is going to make you a great guitarist. In either case, practice makes perfect. 

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The Short Version

If you don't like how your CD's or DVD's sound.....
GET THEM MASTERED!
 
 

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