The last step in audio recording is Mastering. When people ask, “What is mastering?” the answers can be frustratingly mysterious. And when looking at the liner notes of just about any album recorded the last 50 years, the mastering (and re-mastering!) credits are listed separately from the production and engineering credits. So what does mastering do, and how important is it to the final production?

Mastering a piece of audio requires different equipment and acoustic room treatments than what was used to record and mix it. The person mastering a project will go through the final mix, the overall EQ, and volume levels with a fine tooth comb on precision hardware and software dedicated solely to this operation. He/she may also add digital track information  needed for cataloging. The idea is to get the finished audio in perfect order with the best dynamic range and the most uniform volume possible. There are some technical  standards that professional audio must adhere to. That way, it will sound as consistent on a home stereo as it does in a club as it does on the radio or streaming service. All other copies of the result will come from this mastered track. The best analogy I can think of is running your audio through a carwash so it looks a shiny and clean on the outside as the rest of the cars on the lot. Whether or not it runs or not, that depends on what is on the inside and who’s driving it.

An equally important question is: Should every project be mastered? Short answer, no. Mastering costs are separate from recording costs (method).  If you plan to record a demo for your friends to listen to or make an informal piece of audio for a one-off performance, you probably don’t need to master your project. However, let’s say your new song is getting listeners from outside your group of friends or you want to release the song(s) on your streaming page for public download, in that case, because people will be listening to it on different formats, you might consider putting it through the mastering carwash.

Any professional recording made for repeated public broadcast should probably be mastered. From personal experience, mastering usually does make a noticeable difference in quality, especially for a piece of vinyl. Make sure you trust the person mastering the project. This is not a process whereby you sit next to the person and work intimately like you do in recording or mixing. Mastering is done usually off-site and is generally not a collective process. The choice of who does the mastering can be a creative choice as much as a price-conscious one.

I personally have never mastered a project myself. But I have gotten to know people who do engage in this area of audio production. Mastering will take experience and training that is outside the realm of this particular course, but everything learned up to here can apply towards that sort of education. Most of the people I know in that field started out in small studios  or as sound mixers for small clubs/events. After gaining experience and developing finely tuned ears, they decided to venture further in that direction and have done great work in mastering audio ever since.

Below are some expanded definitions of mastering along with some helpful links.

Mandy Parnell: Mastering Audio

Sage Audio: What is Mastering

Mastering

Mastering, a form of audio post production, is the process of preparing and transferring recorded audio from a source containing the final mix to a data storage device (the master), the source from which all copies will be produced (via methods such as pressing, duplication or replication). In recent years digital masters have become usual, although analog masters—such as audio tapes—are still being used by the manufacturing industry, particularly by a few engineers who specialize in analog mastering.

Mastering requires critical listening; however, software tools exist to facilitate the process. Results depend upon the intent of the engineer, the skills of the engineer, the accuracy of the monitors, and the listening environment. Mastering engineers often apply equalization and dynamic range compression in order to optimize sound translation on all playback systems. It is standard practice to make a copy of a master recording—known as a safety copy—in case the master is lost, damaged or stolen.

Process

The source material, ideally at the original resolution, is processed using equalization, compression, limiting and other processes. Additional operations, such as editing, specifying the gaps between tracks, adjusting level, fading in and out, noise reduction and other signal restoration and enhancement processes can also be applied as part of the mastering stage. The source material is put in the proper order, commonly referred to as assembly (or ‘track’) sequencing. These operations prepare the music for either digital or analog, e.g. vinyl, replication.

If the material is destined for vinyl release, additional processing, such as dynamic range reduction or frequency-dependent stereo–to–mono fold-down and equalization may be applied to compensate for the limitations of that medium. For compact disc release, start of track, end of track, and indexes are defined for playback navigation along with International Standard Recording Code (ISRC) and other information necessary to replicate a CD. Vinyl LP and cassettes have their own pre-duplication requirements for a finished master. Subsequently, it is rendered either to a physical medium, such as a CD-R or DVD-R, or to computer files, such as a Disc Description Protocol (DDP) file set or an ISO image. Regardless of what delivery method is chosen, the replicator factory will transfer the audio to a glass master that will generate metal stampers for replication.

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 the following:

1. Transferring the recorded audio tracks into the Digital Audio Workstation (DAW)
2. Sequence the separate songs or tracks as they will appear on the final release
3. Adjust the length of the silence between songs
4. Process or sweeten audio to maximize the sound quality for the intended medium (e.g. applying specific EQ for vinyl)
5. Transfer the audio to the final master format (CD-ROM, half-inch reel tape, PCM 1630 U-matic tape, etc.)

Examples of possible actions taken during mastering:

1. Editing minor flaws
2. Applying noise reduction to eliminate clicks, dropouts, hum and hiss
3. Adjusting stereo width
4. Equalize audio across tracks for the purpose of optimized frequency distribution
5. Adjust volume
6. Dynamic range compression or expansion
7. Peak limit
8. Inserting ISRC codes and CD text
9. Arranging track in their final sequential order
10. Fading out the ending of each song (if required)
11. Dither

 License Link

Pre-Mastering Checklist

Have you:

 Created a mix that’s musically balanced, tonally balanced, and supports the emotion of the song?

 Compared your mix to several references?

 Left enough headroom to avoid clipping?

 Checked the entire mix for clicks and pops? (tip: listen on headphones)

 Turned off any “analog noise” within your plugins? (see image below)

 Removed fade-ins and fade-outs? (unless you’re using an automated service like LANDR, in which case you should leave these in)?

 Exported a high-quality WAV or AIFF file? (no MP3s!)

    Written by Jason Moss, Behind the Speakers