Mastering is an essential but frequently overlooked and misunderstood part of making a great-sounding record. Mastering is the process of transferring audio from your mix master (analog tape, digital file, audio CD, DAT, cassette, etc.) to a medium that can be used for mass duplication (such as a lacquer disc, DDP image, or a Redbook Standard audio CD). In the course of this process, numerous enhancements, edits and alterations can be made, as dictated by the nature of the project and the client's wishes.

Mastering is also an important quality assurance phase of the recording process that offers you the following key benefits:

A Fresh PerspectiveThe opportunity to have a pair of seasoned, experienced ears analyze your mixes on exceptional playback equipment in a well-tuned room. A mastering studio's accurate monitoring can expose flaws in your mixes that had previously not been apparent. Additionally, the mastering engineer approaches your material with fresh ears: he hasn't been listening to the mixes for days or weeks on end, and thus brings a unique and helpful perspective.
Mix First AidThe opportunity to fix problems detected when it's too late to remix (remove clicks and pops, adjust levels, correct frequency imbalances, reduce noise, etc.).
Create an Album with FlowThe opportunity to fine-tune the sequencing of your master, including adjusting or adding fade-ins and fade-outs, crossfades, and space between tracks... even adding tracks from multiple recording sessions in multiple formats to the final album program.
SweeteningThe opportunity to use world-class processing (EQ, compression, limiting, stereo field adjustment, etc.) to enhance your mixes and make them sound even better than the already great mixes you left the studio with. Often it is the work done in this phase of mastering that helps the mastered recording stack up to other commercial recordings in terms of sonic brilliance and overall volume (though I work hard to not make recordings so loud that dynamics, punch and clarity are compromised).
Peace of MindThe opportunity to make an error-free production master that you can be certain the pressing plant will replicate accurately.

In short, mastering is your last opportunity to ensure that the quality of your record will be second to none.