Audio mastering is the final step in audio production, but it’s still a nebulous term which isn’t especially obvious in terms of what it is or why it’s needed. While I’ve always mixed my own music, I started out as an audio mastering engineer professionally before I began mixing professionally shortly after. Let’s demystify and define what is audio mastering – the final step in audio production.
What is Audio Mastering
After the various individual tracks which make up a song have had processing like EQ and compression added to ensure they sound as good as possible, and their levels and panning has been set to ensure they optimally gel as a collective unit, the collection is mixed down and rendered to a single file.
This single file, typically an uncompressed WAV (see types of audio formats for more information), is sent to the mastering engineer for the mastering process.
Audio mastering is the final step in audio production which ensures the song sounds as good as possible and is ready for release. This process includes making any final tonal/balance enhancements, raising the volume to a competitive level without sacrificing quality, and getting the audio ready for whatever format it’s going to be released through (digital/streaming, vinyl, CD, etc.)
Let’s talk about each of those aspects individually for more context and depth to better understand what is audio mastering and what goes into it.
Enhancements
The first job in the audio mastering stage is to decide if any tonal and/or balance adjustments are necessary and if so to make them using plugins like multiband compression or stereo imaging.
Ideally the person who masters a song isn’t the same person who mixed it. This affords the song the opportunity to get a fresh set of ears and perspective to hear potential for improvements to make.
Note that adjustments aren’t necessary on every master; it really depends how good the mixing engineer was at nailing that mix.
As a mastering engineer at MusicGuyMastering.com, even if I hear a couple small changes I’d make, I’ll also oftentimes get clients who don’t want many or any changes to the “sound” of the mix itself.
This is fair; they worked hard to get that mix where they want it, in which case they just want the other aspects of audio mastering which I’ll hit on in a moment.
In the chance that there are any adjustments to make, they should generally be minimal and conservative because we’re affecting the entire mix rather than individual tracks like were available in the mixing stage.
This is a good time to mention that if any problems jump out on specific instruments in the WAV file for the mix, I’ll almost always recommend that a client make those changes on that track on the mix level and resubmit the mixed down file to me because I can’t make changes with that level of granularity in the mastering stage.
Any attempts to fix individual elements of the mixed down file will almost always work to the detriment of another element of the mix at the same time.
Competitive Volume
I always stress the importance of gain staging as well as high and low passing in the mixing stage. Not only do these ultimately make your mix sound better each in their own ways, they both also create mixing headroom.
It’s important that a finished mix be peaking around -6dB at most at the loudest point so that the mastering engineer has some headroom because any processing like I just mentioned will generally raise the volume of that mix.
There’s also no reason to make a mix as loud as possible because mastering engineers have experience with maximizing the volume of a mixed down file without introducing artifacts like distortion and clipping.
While the Loudness War isn’t quite impactful as in the past with most people consuming music through streaming services which typically have normalizing audio as a standard feature, you don’t want your song to be appreciably quieter than its peers.
This is an important aspect of the audio mastering process as the engineer knows the ideal volume based on your song and the streaming services you’re going to be releasing to (see what LUFs to master to).
Format Adherence
Lastly and very importantly, the mastering process gets your song ready for whichever format you’re releasing your music to. Digital, CD, vinyl, etc. – they all have their own requisites.
Digital
Digital music releases are relatively straightforward and don’t require as many considerations. The only thing to keep in mind is the specific bit depth and sample rate which streaming distributors recommend (see what bit depth and sample rate should I use).
CD
The maximum bit depth CDs support is 16 bit. As such, the 24 bit depth your likely recorded and rendered at needs to be reduced. A special process known as audio dithering is used in the mastering stage to avoid the noise associated with forcing your 24 bit audio into a 16 bit package.
In addition to dithering your audio to 16 bit, the mastering engineer also creates a special file set known as a DDP. This contains all of the metadata about your album and songs including the tracklist, song/album name(s), credits, ISRC codes, the UPC code, etc.
This is the file set which CD replication plants use to create the duplicates of your CD without issue.
Vinyl
Vinyl is more popular than it’s been in 35 years, so a lot of artists are opting to also release their music on vinyl.
While you can oftentimes create a vinyl record from the digital masters, there are a few things to keep in mind regarding your normal mix/master which may not translate to vinyl.
See my overview on mastering for vinyl for the full list of considerations which mastering engineers keep in mind when getting a release ready for vinyl.
As you can see, there’s a lot more which goes into audio mastering than simply boosting the volume. Depending on the medium, there can be a lot of additional work required after the mixing phase is concluded to ensure that your music is sounding as good as possible and is ready for a commercial release.
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