Mastering is the process of creating a single or an album master ready for duplication. It is the final creative stage in the process of creating a song or album.

During this process, extra sound processing is usually applied in order to get the sound just right,
to achieve a consistency between the different tracks and to fix any problems from the recording stage.
It’s what makes a record sound like a record as opposed to a collection of songs.

For more details about the mastering process read more about mastering.

The goal of this step is to correct mix balance issues and enhance particular sonic characteristics, taking a good mix (usually in the form of a stereo file) and putting the final touches on it. This can involve adjusting levels and general “sweetening” of the mix. Think of it as the difference between a good-sounding mix and a professional-sounding, finished master.

This process can involve adding broad equalization, applying compression, limiting, etc. This is often actually referred to as “premastering” in the world of LP and CD replication, but let’s refer to it as mastering for simplicity.

Consideration also has to be made for how the individual tracks work together when played one after another in an album sequence. Is there a consistent sound? Are the levels matched? Does the collection have a common “character” and play back evenly so that the listener doesn’t have to adjust the volume?

This process is generally included in the previous step, with the additional evaluation of how individual tracks sound in sequence and in relation to each other. This doesn’t mean that you simply make one preset and use it on all your tracks so that they have a consistent sound. Instead, the goal is to reconcile the differences between tracks while maintaining (or even enhancing) the character of each of them, which will most likely mean different settings for different tracks.

The final step usually involves preparing the song or sequence of songs for download, manufacturing and/or duplication/replication. This step varies depending on the intended delivery format. In the case of a CD, it can mean converting to 16 bit/44.1 kHz audio through resampling and/or dithering, and setting track indexes, track gaps, ISRC codes, and other CD-specific markings. For web-centered distribution, you might need to adjust the levels to prepare for conversion to AAC, MP3 or hi-resolution files and include the required metadata.