Audio mastering is the term used to describe the final steps of a project prior to duplication.
Mastering is a process which requires critical listening skills and an “educated ear”.
So that your audio material can sound its absolute best on a wide variety of devices, from ear buds to stadium speakers, the mastering engineer not only uses many tools and techniques but also depends upon an acoustically balanced environment. The room and playback system(s) must accurately reproduce and process the material.
In most cases, with a good mix, a “light mastering”, often referred to as “pre-mastering”, is probably the perfect solution to your project. It adds the shine your project needs while making your project cd ready but lacks the attention to detail performed by specialized mastering engineers.
This style of mastering is typical of the processing you’ll recieve from any number of mastering services advertising on sites like Craigslist. These services tend to focus mainly on volume enhancement and equalization.
You can get great results, but it’s possible that you’ll get much less than you paid for since results vary radically depending upon the experience, equipment, acoustic environment, and even personal preference of the persons offering such services.
This type of processing is best suited for demos and smaller projects.
Advanced Mastering, often referred to as “production mastering”, is a highly specialized combination of both art and science, and depending upon the scope of the project, and is generally outsourced by recording studios.
With professional mastering, a complex process begins in a finely tuned room with specialized equipment. The audio is prepared by a highly skilled engineer for duplication as tracks are sequenced and fades and edits are made. A great degree of attention is then paid to frequency and instrument enhancement, loudness and dynamic range, psycho-acoustics, stereo imaging, mid/side processing, automation, and phase alignment. Overall ambient effects are also blended in. Noise reduction, cancellation and dithering is applied. The mastered tracks are then prepared for duplication. DDP and ISRC Sub-code is added. Logs are prepared, UPC codes are generated, and files are tagged. The production mastering process might also include the addition of pre-rolls, images, and other additional data as required. Several separate masters of the same material might even be prepared to meet differing industry standards.
Mastering is ordinarily applied to the stereo mixdown of a session. With access to individual tracks or groups of tracks, a process called Separation Mastering can be performed. This ability to achieve such detailed processing and editing can further refine the character of your mix.