Do you know the final process that takes place in an album production? Before the CDs of your favourite artists are mass produced for the consumer market, every song in the album has to first be professionally prepared. If you are serious about producing music or simply just a curious music fan, then you must ask – What is “Mastering” in Audio?
In my opinion, the subject that we will be discussing in today’s article, is one that is seldom touched on in the academic sphere (especially in entry-level music technology courses). I will try my best to give you a comprehensive overview, so that you’ll have a decent understanding of the whole process. You ready to learn more? Me too!
Audio Mastering – A Vital Process
Basically an audio post production process, mastering involves the preparation of recorded audio, and transferring it from a source (that stores the final mix) to a data storage device such as a CD or DVD (also known as the “master”). This “master” will then be mass produced for the consumer market using methods such as pressing, duplication or replication.
Today, digital masters are the most common ones. However, analog masters such as audio tapes, are still being utilised in the industry, typically by a handful of engineers who specializes in analog mastering. Critical listening skills and various software tools are required for mastering, but the results still depend on the loudspeaker’s quality and listening environment.
In some cases, mastering engineers have to apply audio production techniques such as “corrective equalization” and “dynamic compression” in order to ensure optimum sound reproduction quality on all playback systems. A copy of the original master is always made, in case it gets lost, damaged or stolen. This duplicate master is known as the “safety copy”.
Let us look at the various topics that we’ll be covering:
- Digital technology
- Processing stages
Nowadays, most mastering works are done digitally, with recordings stored on hard disk drives and transferred to CDs. The digital audio workstation (DAW) is at the core of many mastering facilities, where a combination of digital and analog processing tools and devices are used. Engineers always debate the use of digital versus analog signal processing during mastering.
There isn’t really any “optimum mix level” for mastering. However, there is a rough guideline for the ideal mix levels that studio and mastering engineers should adhere to. When it comes to mastering, it is vital that enough headroom is allowed for the master engineer to work with. The reduction of headroom by mastering engineers has caused a “loudness war” in the industry.
The audio track (that is to be mastered) is processed using equalizers, compressors, limiters and other signal processors. Tasks such as editing, fading in and out, noise reduction and other signal restoration and enhancement processes can also be done during the mastering process. This stage prepares the music for either digital or analog (e.g. vinyl) duplication.
Every track in the album will then be arranged in the correct order (also known as “track sequencing”). If the tracks are prepared for vinyl release, then additional audio compression and equalization, may be needed to optimise the sound quality for that medium. As for a compact disc release, the “Start of Track”, “End of Track”, and “Indexes” are inserted for disc navigation.
The tracks (for compact disc release) are then rendered to a physical CD-R or DVD-R, or to computer files, such as a Disc Description Protocol (DDP) file set or an ISO file. The final medium will vary, depending on the chosen final release format of the product. For example, a digital audio release may have multiple master mediums, chosen based on replication factory requirements or record label security issues.
The specific steps taken during an audio mastering session will vary depending on the requirements of the audio to be processed. Mastering engineers need to first consider the types of input media, the perspective of the album’s producer or consumer and the technical limitations of the various playback mediums, before starting any mastering project.
Here are the general steps taken during mastering:
- Recorded audio tracks to be imported into the Digital Audio Workstation (DAW)
- All songs or tracks to be sequenced just like how they will appear on the final release
- The length of “silence” in between songs are adjusted
- Audio to be processed or “polished” to maximize the sound quality for the intended medium (e.g. applying specific EQ for vinyl)
- Transferring the audio to the final master format (CD-ROM, half-inch reel tape, PCM 1630 U-matic tape, etc.)
Here are the possible processing or editing steps taken during mastering:
- Editing minor flaws
- Eliminate clicks, dropouts, hum and hiss by using noise reduction
- Attenuating the stereo width
- Applying effects such as “reverb” to add ambience
- Optimizing frequency distribution across all tracks by using equalizers
- Making adjustments to volume levels
- Dynamic range compression or expansion
- Peak limit (using a “limiter”)
- Dither (to prevent quantization distortion in digital audio filters)
To finalise the mastering process of a CD, track markers must be inserted, along with International Standard Recording Code (ISRC) and other information necessary to replicate a CD. Take note that vinyl LP and cassettes have their own pre-duplication requirements for a finished master.
There you have it, an overview of the whole mastering process. I hope this has been very educational and helpful for you folks. So, are any of you aspiring to be a mastering engineer now?
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