Editing Mastering (audio)

{{Short description|Form of audio post-production}}
{{Use American English|date=February 2020}}

[[File:Reel-to-ReelTapeBigHub.agr.jpg|thumb|[[Magnetic tape]] was commonly used to create master copies.]]

'''Mastering''', a form of [[audio post production]], is the process of preparing and transferring recorded audio from a source containing the [[Audio mixing (recorded music)|final mix]] to a [[data storage device]] (the [[Master recording|master]]), the source from which all copies will be produced (via methods such as pressing, duplication or [[Replication (optical media)|replication]]). In recent years, [[digital master]]s 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.<ref>{{cite web|url=https://thevinylfactory.com/features/analogue-digital-vinyl-mastering-interviews/ |title=What's actually going on when people talk about digital vs. analogue masters|date=18 October 2017 }}</ref>

Mastering requires critical listening; however, software tools exist to facilitate the process. Results depend upon the intent of the engineer, their skills, the accuracy of the speaker monitors, and the listening environment. '''Mastering engineers''' often apply [[Equalization (audio)|equalization]] and [[dynamic range compression]] in order to optimize sound translation on all playback systems.<ref name="mixmagazine" /> 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.

==History==

===Pre-1940s===
In the earliest days of the recording industry, all phases of the recording and mastering were entirely mechanical processes. Performers sang or played into a large [[acoustic horn]] and the master recording was created by the transfer of acoustic energy from the [[Diaphragm (acoustics)|diaphragm]] of the recording horn to the [[mastering lathe]], typically located in an adjoining room. The cutting head, driven by the energy from the horn, inscribed a modulated groove into the surface of a rotating cylinder or disc.<ref name=Auld>{{cite magazine |url=http://www.recordingmag.com/resources/resourceDetail/109.html |title=Mastering Then and Now |author=Robert Auld |magazine=Recording |access-date=2016-01-19 |archive-url=https://web.archive.org/web/20171124115019/http://www.recordingmag.com/resources/resourceDetail/109.html |archive-date=2017-11-24 |url-status=dead }}</ref> These masters were usually made from either a soft metal alloy or from [[wax]]; this gave rise to the colloquial term ''waxing'', referring to the cutting of a record.<ref>{{citation |url=https://books.google.com/books?id=k_UDAAAAMBAJ&pg=PA47 |title=New Technique Aids LP Waxing |magazine=[[Billboard (magazine)|Billboard]] |date=1950-03-25}}</ref>

After the introduction of the [[microphone]] and [[electronic amplifier]] in the mid-1920s, the mastering process became electro-mechanical, and electrically driven mastering lathes came into use for cutting master discs (the cylinder format by then having been superseded). Until the introduction of tape recording, master recordings were almost always cut [[Direct to disc recording|direct-to-disc]].<ref name=Auld/> Only a small minority of recordings were mastered using previously recorded material sourced from other discs.

===Emergence of magnetic tape===
In the late 1940s, the recording industry was revolutionized by the introduction of [[magnetic tape]]. Magnetic tape was invented for recording sound by [[Fritz Pfleumer]] in 1928 in Germany, based on the invention of [[magnetic wire recording]] by [[Valdemar Poulsen]] in 1898.  Not until the end of [[World War II]] could the technology be found outside Europe. The introduction of magnetic tape recording enabled master discs to be cut separately in time and space from the actual recording process.<ref name=Auld/>

Although tape and other technical advances dramatically improved the audio quality of commercial recordings in the post-war years, the basic constraints of the electro-mechanical mastering process remained, and the inherent physical limitations of the main commercial recording media—the 78 rpm disc and later the 7-inch 45 rpm single and 33-1/3 rpm [[Gramophone record|LP record]]—meant that the audio quality, [[dynamic range]],{{efn|Dynamic range was limited by the fact that if the mastering level was set too high, the cutting head might be damaged during the cutting process or the stylus may jump out of the groove during playback.<ref name=Auld/>}} and running time{{efn|Running times were constrained by the diameter of the disc and the density with which grooves could be inscribed on the surface without cutting into each other.}} of master discs were still limited compared to later media such as the [[compact disc]].

===Electro-mechanical mastering process===
From the 1950s until the advent of digital recording in the late 1970s, the mastering process typically went through several stages. Once the studio recording on multi-track tape was complete, a final [[Audio mixing (recorded music)|mix]] was prepared and dubbed down to the master tape, usually either a single-track [[Monaural|mono]] or two-track [[stereo]] tape. Prior to the cutting of the master disc, the master tape was often subjected to further electronic treatment by a specialist mastering engineer.

After the advent of tape it was found that, especially for pop recordings, master recordings could be made so that the resulting record would sound better. This was done by making fine adjustments to the amplitude of sound at different frequency bands ([[Equalization (audio)|equalization]]) prior to the cutting of the master disc.

In large recording companies such as [[EMI]], the mastering process was usually controlled by specialist staff technicians who were conservative in their work practices. These big companies were often reluctant to make changes to their recording and production processes. For example, EMI was very slow in taking up innovations in [[multi-track recording]]{{efn|In [[multi-track recording]] each signal input is recorded to its own track on a multi-track recorder. This multi-track tape is mixed down to a mono or stereo master tape. A multi-track tape may be remixed many times, in different ways, by different engineers, giving the possibility of several masters (mono version, stereo version, LP version, AM radio version, single version, etc.).}} and did not install 8-track recorders in their [[Abbey Road Studios]] until the late 1960s, more than a decade after the first commercial 8-track recorders were installed by American independent studios.<ref>{{cite book|last1=Martin|first1=George|author-link1=George Martin|last2=Hornsby|first2=Jeremy|title=All you need is ears|year=1994|publisher=Macmillan|isbn=0-312-11482-6|page=143}}</ref>

===Digital technology===
[[File:Optimum-mix-levels-for-mast.jpg|thumb|240px|right|Optimum Digital Levels with respect to the Full Digital Scale (dBFSD)]]
In the 1990s, electro-mechanical processes were largely superseded by digital technology, with [[digital recording]]s stored on [[hard disk drive]]s or digital tape and mastered to [[CD]]. The [[digital audio workstation]] (DAW) became common in many mastering facilities, allowing the off-line manipulation of recorded audio via a [[graphical user interface]] (GUI).  Although many digital processing tools are common during mastering, it is also very common to use analog media and processing equipment for the mastering stage. Just as in other areas of audio, the benefits and drawbacks of [[Comparison of analog and digital recording|digital technology compared to analog technology]] are still a matter for debate. However, in the field of audio mastering, the debate is usually over the use of digital versus analog signal processing rather than the use of digital technology for storage of audio.<ref name="mixmagazine">{{cite magazine |url=http://mixonline.com/recording/mastering/audio_issues_modern_mastering |magazine=Mix Magazine |title=Issues in Modern Mastering |archive-url=https://web.archive.org/web/20070524113354/http://mixonline.com/recording/mastering/audio_issues_modern_mastering/ |archive-date=May 24, 2007 |date=May 1, 2006 |author=Blair Jackson}}</ref>

Digital systems have higher performance and allow mixing to be performed at lower maximum levels. When mixing to 24-bits with peaks between −3 and −10 dBFS on a mix, the mastering engineer has enough [[Headroom (audio signal processing)|headroom]] to process and produce a final master.<ref name="bob_katz">[http://www.digido.com/bob-katz/mixing-tips-and-tricks.html Bob Katz Mixing Tips] {{webarchive |url=https://web.archive.org/web/20070827154625/http://www.digido.com/bob-katz/mixing-tips-and-tricks.html |date=August 27, 2007 }}</ref> Mastering engineers recommend leaving enough headroom on the mix to avoid distortion.<ref>[http://cdmusicmastering.com/how-much-headroom-for-mastering.html How much headroom for mastering?]</ref> The reduction of dynamics by the mix or mastering engineer has resulted in a [[loudness war]] in commercial recordings.<ref name="Shelvock" />

== Process ==
[[File:Manleyvarimu.jpg|thumb|A common mastering processor for [[dynamic range compression]]]]
The source material, ideally at the original [[Audio bit depth|resolution]], is processed using equalization, [[Dynamic range compression|compression]], [[limiting]] and other processes. Additional operations, such as [[editing]], specifying the gaps between tracks, adjusting level, fading in and out, [[Audio noise reduction|noise reduction]] and other signal restoration and enhancement processes can also be applied as part of the mastering stage.<ref name="Shelvock">{{Cite book|title = Audio Mastering as Musical Practice|last = Shelvock|first = Matt|publisher = ETDR: University of Western Ontario|year = 2012|location = Ontario, Canada|pages = 1–72|url = http://ir.lib.uwo.ca/cgi/viewcontent.cgi?article=1709&context=etd}}</ref> 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 [[Cassette tape|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 [[Compact Disc manufacturing|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:
# Transferring the recorded audio tracks into the [[Digital Audio Workstation ]](DAW)
# Sequence the separate songs or tracks  as they will appear on the final release
# Adjust the length of the silence between songs
# Process or [[Sweetening (show business)|sweeten]] audio to maximize the sound quality for the intended medium (e.g. applying specific equalization for vinyl)
# Transfer the audio to the final master format (CD-ROM, half-inch reel tape, [[U-matic#Digital audio|PCM 1630 U-matic tape]], etc.)

Examples of possible actions taken during mastering:<ref name="Shelvock" />
# Editing minor flaws
# Applying [[noise reduction]] to eliminate clicks, dropouts, hum and hiss
# Adjusting stereo width
# Equalize audio across tracks for the purpose of optimized frequency distribution
# Adjust volume
# Dynamic range compression or expansion
# [[Limiter|Peak limit]]
# Inserting [[ISRC]] codes and CD text
# Arranging tracks in their final sequential order
# Fading out the ending of each song
# [[Dither]]

==Engineer==
{{Multiple issues|section=yes|
{{Refimprove|section|date=October 2008}}
{{Original research|section|date=February 2022}}
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[[File:Doug Sax with 4 Lathes.jpg|thumb|Mastering engineer Doug Sax with four [[disc cutting lathe]]s]]
A '''mastering engineer''' is a person skilled in the practice of taking [[sound|audio]] (typically musical content) that has been previously mixed in either the [[Analog recording|analogue]] or [[digital recording|digital]] domain as mono, stereo, or multichannel formats and preparing it for use in [[Distribution (business)|distribution]], whether by physical media such as a CD, vinyl record, or as some method of streaming audio.

===Education and experience===
The mastering engineer is responsible for a final edit of a product and preparation for manufacturing copies. Although there are no official requirements to work as an audio mastering engineer, practitioners often have comprehensive domain knowledge of audio engineering, and in many cases, may hold an audio or acoustic engineering [[academic degree|degree]]. Most [[audio engineer]]s master music or speech audio material. The best mastering engineers might possess [[arrangement]] and production skills, allowing them to troubleshoot [[Audio mixing (recorded music)|mix]] issues and improve the final sound. Generally, good mastering skills are based on experience, resulting from many years of practice.

===Equipment===
Generally, mastering engineers use a combination of specialized audio-signal processors, low-distortion-high-bandwidth loudspeakers (and corresponding amplifiers with which to drive them), within a dedicated, acoustically-optimized playback environment. The equipment and processors used within the field of mastering are almost entirely dedicated to the purpose; engineered to a high standard, often possessing low signal-to-noise ratios [at nominal operating levels] and in many cases, the incorporation of parameter-recall, such as indented potentiometers, or in some more-sophisticated designs, via a digital-controller. Some advocates for digital software claim that plug-ins are capable of processing audio in a mastering context, though without the same degree of signal degradation as those introduced from processors within the analog domain. The quality of the results varies according to the algorithms used within these processors, which in some cases, can introduce distortions entirely exclusive to the digital domain.

[[Real-time analyzer]]s, phase [[oscilloscope]]s, and also peak, RMS, VU and K meters are frequently used within the audio analysis stage of the process as a means of rendering a visual representation of the audio, or signal, being analyzed.

===Aspects of their work===
Most mastering engineer accolades are given for their ability to make a mix consistent with respect to subjective factors based on the perception of listeners, regardless of their playback systems and the environment. This is a difficult task due to the varieties of systems now available and the effect it has on the apparent qualitative attributes of the [[Sound recording and reproduction|recording]]. For instance, a recording that sounds great on one [[Loudspeaker|speaker]]/[[amplifier]] combination playing CD audio, may sound drastically different on a computer-based system playing back a low-[[bitrate]] [[MP3]]. Some engineers maintain that the main mastering engineer's task is to improve upon playback systems translations while the position of others is to make a sonic impact.<ref name="edward_vinatea">{{cite web |url=http://musicmasteringonline.com/understanding-mastering/ |title=Understanding Mastering |last=Vinatea |first=Edward |date=24 April 2010 |website=The Directory of Mastering Studios |access-date=2 February 2018}}</ref>

Prolonged periods of listening to improperly mastered recordings usually leads to hearing fatigue that ultimately takes the pleasure out of the listening experience.<ref name="stylusmagazine"> {{cite magazine |last=Southall |first=Nick |date=1 May 2006 |title=Imperfect Sound Forever |url=http://www.stylusmagazine.com/articles/weekly_article/imperfect-sound-forever.htm |magazine=Stylus |archive-url=https://web.archive.org/web/20171203075701/http://www.stylusmagazine.com/articles/weekly_article/imperfect-sound-forever.htm |archive-date=3 December 2017 |access-date=2 February 2018 |url-status=dead}}</ref>

===Notable audio mastering engineers===
{{div col|colwidth=20em}}
*[[Brad Blackwood]]
*[[Greg Calbi]]
*[[Tony Dawsey]]
*[[P. A. Deepak]]
*[[Brian Gardner]]
*[[Chris Gehringer]]
*[[Kevin Gray (mastering engineer)|Kevin Gray]]
*[[Bernie Grundman]]<ref>{{cite news |url=https://www.latimes.com/entertainment/music/la-et-ms-bernie-grundman-mastering-red-bull-20171022-story.html |last=Wood |first=Mikael |title=Bernie Grundman wants to change the way you hear music — for the better |work=Los Angeles Times |date=2017-10-27 |access-date=2020-01-26}}</ref>
*[[Steve Hoffman (audio engineer)|Steve Hoffman]]<ref>{{cite magazine|url=https://tapeop.com/articles/85/steve-hoffman/ |last=Hanlon |first=Keith |title=Steve Hoffman: Mastering The Beach Boys, Miles Davis, & More |magazine=TapeOp Magazine |date=September–October 2011 |access-date=2020-01-26}}</ref>
*[[Ted Jensen]]
*[[Bob Katz]]
*[[Heba Kadry]]
*[[Emily Lazar]]
*[[Bob Ludwig]]
*[[Stephen Marcussen]]
*[[George Marino]]<ref>{{cite news |url=https://www.hollywoodreporter.com/news/george-marino-legendary-mastering-engineer-333020 |last=Barnes |first=Mike |title=George Marino, Legendary Mastering Engineer, Dies |work=Hollywood Reporter |date=2012-06-04 |access-date=2020-01-26}}</ref>
*[[Randy Merrill]]
*[[Mandy Parnell]]
*[[George Peckham|George "Porky" Peckham]]
*[[Eric Pillai]]<ref>{{cite web|url=http://ericpillai.com/site/|title=Eric Pillai – Future Sound of Bombay}}</ref>
*[[Shadab Rayeen]]
*[[Doug Sax]]
*[[H. Sridhar]]
*[[Ray Staff]]
*[[Rudy Van Gelder]]
*[[Howie Weinberg]]
*[[Leon Zervos]]
{{div col end}}

== See also ==
* [[Grammy Award for Best Surround Sound Album]]
* [[PMCD]]
* [[Loudness war]]
* [[Album era]]
* [[Remaster]]
* [[2008 Universal Studios fire]]

==Notes==
{{Notelist}}

== References ==
{{Reflist}}

{{Music production}}
{{Authority control}}

{{DEFAULTSORT:Audio Mastering}}
[[Category:Audio engineering]]
[[Category:Mastering engineers| ]]
[[Category:Optical disc authoring]]
[[Category:Sound recording]]
[[Category:Music industry]]