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{{Short description|Audio mixing to yield recorded sound}}
[[File:Sony DMXR100.jpg|thumb|300px|Digital Mixing Console Sony DMX R-100 used in project studios]]
In [[sound recording and reproduction]], '''audio mixing''' is the process of optimizing and combining [[multitrack recording]]s into a final [[monaural|mono]], [[stereo]] or [[surround sound]] product. In the process of combining the separate tracks, their relative levels are adjusted and balanced and various processes such as [[equalization (audio)|equalization]] and [[dynamic range compression|compression]] are commonly applied to individual tracks, groups of tracks, and the overall mix. In stereo and surround sound mixing, the placement of the tracks within the stereo (or surround) field are adjusted and balanced.<ref name="Huber, 5th ed." />{{rp|11,325,468}} Audio mixing techniques and approaches vary widely and have a significant influence on the final product.<ref>{{cite book|last1=Strong|first1=Jeff|title=Home Recording For Musicians For Dummies|date=2009|publisher=Wiley Publishing, Inc.|location=Indianapolis, Indiana|page=249|edition=Third}}</ref>
Audio mixing techniques largely depend on [[music genre]]s and the quality of sound recordings involved.<ref>{{cite book|last1=Hepworth-Sawyrr|first1=Russ|title=From Demo to Delivery. The production process|date=2009|publisher=Focal Press|location=Oxford, United Kingdom|page=109}}</ref> The process is generally carried out by a [[mixing engineer]], though sometimes the [[record producer]] or [[recording artist]] may assist. After mixing, a [[mastering engineer]] prepares the final product for production.
Audio mixing may be performed on a [[mixing console]] or in a [[digital audio workstation]].
==History==
In the late 19th century, [[Thomas Edison]] and [[Emile Berliner]] developed the first recording machines. The recording and reproduction process itself was completely mechanical with little or no electrical parts. Edison's [[phonograph cylinder]] system utilized a small horn terminated in a stretched, flexible diaphragm attached to a stylus which cut a groove of varying depth into the malleable tin foil of the cylinder. Emile Berliner's gramophone system recorded music by inscribing spiraling lateral cuts onto a vinyl disc.<ref>{{cite book|last1=Rumsey|first1=Francis|last2=McCormick|first2=Tim|title=Sound and Recording|url=https://archive.org/details/soundrecording00rums|url-access=limited|date=2009|publisher=Elsevier Inc.|location=Oxford, United Kingdom|isbn=978-0-240-52163-3|page=[https://archive.org/details/soundrecording00rums/page/n192 168]|edition=6th}}</ref>
Electronic recording became more widely used during the 1920s. It was based on the principles of electromagnetic [[transducer|transduction]]. The possibility for a microphone to be connected remotely to a recording machine meant that microphones could be positioned in more suitable places. The process was improved when outputs of the microphones could be mixed before being fed to the disc cutter, allowing greater flexibility in the balance.<ref>{{cite book|last1=Rumsey|first1=Francis|last2=McCormick|first2=Tim|title=Sound and Recording|url=https://archive.org/details/soundrecording00rums|url-access=limited|date=2009|publisher=Elsevier Inc.|location=Oxford, United Kingdom|isbn=978-0-240-52163-3|page=[https://archive.org/details/soundrecording00rums/page/n193 169]|edition=6th}}</ref>
Before the introduction of [[multitrack recording]], all sounds and effects that were to be part of a recording were mixed simultaneously during a live performance. If the recorded mix was not satisfactory, or if one musician made a mistake, the selection had to be performed over until the desired balance and performance was obtained. The introduction of multi-track recording changed the recording process into one that generally involves three stages: [[sound recording and reproduction|recording]], [[overdubbing]], and mixing.<ref name=Huber>{{cite book |author=Huber, David Miles |date=2001 |title=Modern Recording Techniques |page=[https://archive.org/details/modernrecordingt00davi/page/321 321] |publisher=Focal Press |isbn=978-0240804569 |url=https://archive.org/details/modernrecordingt00davi/page/321 }}</ref>
Modern mixing emerged with the introduction of commercial multi-track tape machines, most notably when [[multitrack recording|8-track recorders]] were introduced during the 1960s. The ability to record sounds into separate channels made it possible for recording studios to combine and treat these sounds not only during recording, but afterward during a separate mixing process.<ref>{{Cite web|url=http://www.liverpoolmuseums.org.uk/wml/exhibitions/thebeatgoeson/thebeatgoesonline/technology/studios/multitrack.aspx|title=The emergence of multitrack recording|access-date=June 17, 2018}}</ref>
The introduction of the [[Cassette tape|cassette-based]] [[Portastudio]] in 1979 offered multi-track recording and mixing technology that did not require the specialized equipment and expense of commercial recording studios. [[Bruce Springsteen]] recorded his 1982 album ''[[Nebraska (album)|Nebraska]]'' with one, and the [[Eurythmics]] topped the charts in 1983 with the song "[[Sweet Dreams (Are Made of This)]]", recorded by band member [[Dave Stewart (Eurythmics)|Dave Stewart]] on a makeshift 8-track recorder.<ref>[https://musicianguide.com/biographies/1608002793/Eurythmics.html/ Eurythmics Biography]. Musicianguide</ref> In the mid-to-late 1990s, computers replaced tape-based recording for most home studios, with the [[Power Macintosh]] proving popular.<ref>{{cite web|url=http://www.studiorecordingsoftware101.com/ |title=Studio Recording Software: Personal And Project Audio Adventures |year=2008 |publisher=studiorecordingsoftware101.com |access-date=March 20, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20110208092848/http://studiorecordingsoftware101.com/ |archive-date=February 8, 2011 }}</ref> In the mid-1980s, many professional recording studios began to use [[digital audio workstation]]s (DAWs) to accomplish recording and mixing previously done with multitrack tape recorders, mixing consoles, and outboard gear.
==Equipment==
===Mixing consoles===
[[File:Mixing Console Discom2.jpg|thumb|A simple mixing console]]
{{Main|Mixing console}}
A mixer ([[mixing console]], mixing desk, mixing board, or software mixer) is the operational heart of the mixing process.<ref name=White>{{Cite book |title= Creative Recording |last= White |first= Paul |publisher= Sanctuary Publishing |page= [https://archive.org/details/creativerecordin0000whit/page/335 335] |edition= 2nd |year= 2003 |isbn= 978-1-86074-456-3 |url= https://archive.org/details/creativerecordin0000whit/page/335 }}</ref> Mixers offer a multitude of inputs, each fed by a track from a multitrack recorder. Mixers typically have 2 main outputs (in the case of two-channel stereo mixing) or 8 (in the case of surround).
Mixers offer three main functionalities.<ref name="White" /><ref name=Izhaki>{{Cite book |title= Mixing Audio |last= Izhaki |first= Roey |publisher= Focal Press |page= 566 |year= 2008 |isbn= 978-0-240-52068-1 }}</ref>
# Summing signals together, which is normally done by a dedicated summing amplifier or, in the case of a digital mixer, by a simple algorithm.
# Routing of source signals to internal buses or external processing units and effects.
# On-board processors with equalizers and compressors.
Mixing consoles can be large and intimidating due to the exceptional number of controls. However, because many of these controls are duplicated (e.g. per input channel), much of the console can be learned by studying one small part of it. The controls on a mixing console will typically fall into one of two categories: processing and configuration. Processing controls are used to manipulate the sound. These can vary in complexity, from simple level controls, to sophisticated outboard reverberation units. Configuration controls deal with the signal routing from the input to the output of the console through the various processes.<ref name="Holman">{{cite book|last1=Holman|first1=Tomlinson|title=Sound for Film and Television|date=2010|publisher=Elsevier Inc|location=Oxford, United Kingdom|isbn=978-0-240-81330-1|edition=3rd}}</ref>
[[Digital audio workstation]]s (DAW) can perform many mixing features in addition to other processing. An [[audio control surface]] gives a DAW the same user interface as a mixing console.<ref name="Holman" />
===Outboard and plugin-based processing===
Outboard audio processing units (analog) and software-based [[audio plug-in]]s (digital) are used for each track or group to perform various [[Audio signal processing|processing]] techniques. These processes, such as equalization, compression, sidechaining, stereo imaging, and saturation are used to make each element as audible and sonically appealing as possible. The mix engineer also will use such techniques to balance the ''space'' of the final audio wave; removing unnecessary frequencies and volume spikes to minimize the interference or ''clashing'' between each element.
===Processes that affect signal volume or level===
*[[Fader (audio engineering)|Faders]]&nbsp;– The process of attenuating (lowering) the level of a signal.  This is by far the most basic audio process, appearing on virtually every effect unit and mixer.<ref name=Holman/>{{rp|177}} Utilizing controlled fades is the most basic step of audio mixing, allowing more volume for prominent elements and less for secondary elements.
*Boost&nbsp;– The process of amplifying a signal. Boosting is usually done using extremely slight amounts of amplification, enough to raise a signal without pushing it to the point of distortion. However, when using audio tape as opposed to recording on to a computer, sometimes a signal will be deliberately overdriven very hard to achieve an intense yet soft, 'rounded off' style of distortion known as tape saturation. Distortion from ''clipping'' (overdriving) a digital signal will simply result in blasts of apparent white noise, and is almost universally regarded as unpalatable. Volume control units typically feature the ability to both boost and attenuate a signal.<ref name=Holman/>{{rp|177}}
*[[Panning (audio)|Panning]]&nbsp;– The process of altering the balance of an audio signal between the left and right channels of a stereo signal. The pan of a signal may be modified via a simple two-way pan control or an ''auto panner'' that continuously modulates and changes the pan of a signal.<ref name="Huber, 5th ed.">{{cite book |last1=Huber |first1=David Miles |last2=Runstein |first2=Robert E. |title=Modern recording techniques |publisher=Focal Press |isbn=0-240-80456-2 |edition=5th |date=2001 |url=https://archive.org/details/modernrecordingt00davi }}</ref>{{rp|49,344}} Panning is often used in the mixing process to ''arrange'' the track elements, simulating the placement of live bands.
*[[Dynamic range compression|Compressors]]&nbsp;– The process of reducing the dynamic range or difference between loudest and quietest parts of a signal. This is done by reducing the signal volume after a user-adjustable threshold is hit. The ratio of reduction to gain above the threshold is often also controllable, as well as the time it takes for reduction to activate (attack) or release. Most compressors will also have a makeup gain control, used to apply a boost after the gain reduction is replied to compensate for the quieter signal. Compression has many uses in the mixing process, from evening out vocal volume to enhancing drums.<ref name=Holman/>{{rp|175}}
*[[Limiter]]s&nbsp;– Using a compression ratio of 10:1 or higher is known as limiting- instead of applying gentle reduction to audio above the threshold, limiters forcibly ''flatten'' it down, allowing no signal above the threshold. Many limiting units also have built-in compressors that reduce the amount of audio actually passing the threshold. Many limiters also use digital algorithms to ''soften'' the harsh sound of limited audio, morphing the wave instead of completely decapitating it (by removing part of the waveform entirely, intense distortion and vastly altered tones can occur.) Softer limiters are used with generous amounts of compression to create a more consistently loud track with less volume fluctuation, and harder limiters can be used as distortion effects or emergency safeties to protect large speaker systems from blowing out. Many analog amplifiers are fitted with their own basic limiters to prevent the high-voltage circuitry from overloading and blowing out.<ref name=Holman/>{{rp|176}}
*Dynamic expansion&nbsp;– Expansion <ref name=Holman/>{{rp|176}} Dynamic expansion is essentially compression with an inverted threshold- any signal below a certain threshold is dynamically reduced while signals above the threshold remain untouched. Expansion is most commonly used to give volume to certain elements of recordings- e.g. the bass drum and snare drum. Expanders can also be set up so that when a signal drops below a set threshold, it will reduce gain until the output signal is forced below a certain level, and continue to hold the gain at that level until the input rises above the threshold. This application of expansion is called gating.
===Processes that affect frequencies===
The frequency response of a signal represents the amount (volume) of every frequency in the human [[hearing range]], consisting of (on average) frequencies from 20&nbsp;Hz to 20,000&nbsp;Hz (20&nbsp;kHz.) There are a variety of processes commonly used to edit frequency response in various ways.
*'''[[Equalization (audio)|Equalization]]'''&nbsp;– Equalization is a broad term for any device that can alter parts of a signal frequency response. Some EQs use a grid of faders or knobs which can be arranged to shape each frequency, whereas others use bands that can target and subsequently boost or cut selectable series of frequencies.
<ref name=Holman/>{{rp|178}}
*'''[[Audio filter|Filters]]'''&nbsp;– Filters attenuate part of the audio spectrum. There are various types of filters. A [[high-pass filter]] (low-cut) is used to remove unneeded bass from a sound source. A [[low-pass filter]] (high-cut) is used to remove unneeded treble. These are most often used as a way to ''declutter'' a given mix to improve the clarity of the individual elements. A [[band-pass filter]] is a combination of high- and low-pass filters, also known as a telephone filter (because a sound lacking in high and low frequencies resembles the quality of sound over a telephone).<ref name="Sound and Recording">{{cite book|last1=Rumsey|first1=Francis|last2=McCormick|first2=Tim|title=Sound and Recording|url=https://archive.org/details/soundrecording00rums|url-access=limited|date=2009|publisher=Elsevier Inc.|location=Oxford, United Kingdom|isbn=978-0-240-52163-3|page=[https://archive.org/details/soundrecording00rums/page/n414 390]|edition=6th}}</ref>
===Processes that affect time===
*'''[[Reverb]]s'''&nbsp;– Reverbs are used to simulate acoustic reflections in a real room, adding a sense of space and depth to otherwise ''dry'' recordings. Another use is to distinguish among auditory objects; all sound having one reverberant character will be categorized together by human hearing in a process called [[auditory streaming]]. This is an important technique in creating the illusion of layered sound from in front of the speaker to behind it.<ref name=Holman/>{{rp|181}} Before the advent of electronic reverb and echo processing, physical means were used to generate the effects. An [[echo chamber]], a large reverberant room, could be equipped with a speaker and microphones. Signals were then sent to the speaker and the reverberation generated in the room was picked up by the two microphones.<ref name="Sound and Recording"/>
===Processes that affect space===
*'''[[Panning (audio)|Panning]]'''&nbsp;– While panning is a [[#Processes that affect levels|process that affects levels]], it also can be considered a process that affects space since it is used to give the impression of a source coming from a particular direction. Panning allows the engineer to place the sound within the [[stereo]] or [[Surround sound|surround]] field, giving the illusion of a sound's origin having a physical position.<ref name="Huber, 5th ed." />
*'''{{vanchor|Pseudostereo}}''' creates a stereo-like sound image from monophonic sources. This way the [[apparent source width]] or the degree of [[listener envelopment]] is increased. A number of pseudostereo recording and mixing techniques are known from the viewpoint of audio engineers<ref>{{cite book |last1=Levinit |first1=Daniel J. |editor1-last=Greenbaum |editor1-first=Ken |editor2-last=Barzel |editor2-first=Ronen |title=Audio Anecdotes |date=2004 |publisher=A K Peters |location=Natick |pages=147–158 |chapter=Instrument (and vocal) recording tips and tricks}}</ref><ref name="csound">{{cite journal |last1=Cabrera |first1=Andrés |title=Pseudo-Stereo Techniques. Csound Implementations |journal=CSound Journal |date=2011 |volume=2011 |issue=14 |pages=Paper number 3 |url=http://csoundjournal.com/issue14/PseudoStereo.html |access-date=1 June 2018}}</ref> and researchers.<ref>{{cite conference |url=http://www.aes.org/e-lib/browse.cfm?elib=13193 |title=Pseudostereophony Revisited |first=Christof |last=Faller |year=2005 |conference=Audio Engineering Society Convention 118 |conference-url=http://www.aes.org/events/118/ |location=Barcelona |format=PDF |access-date=1 June 2018 |ref=faller}}</ref><ref name="ziemer">{{cite book |last1=Ziemer |first1=Tim |chapter-url=https://link.springer.com/chapter/10.1007/978-3-319-47292-8_10 |title=Studies in Musical Acoustics and Psychoacoustics |date=2017 |publisher=Springer |isbn=978-3-319-47292-8 |editor1-last=Schneider |editor1-first=Albrecht |series=Current Research in Systematic Musicology |volume=4 |location=Cham |pages=299–340 |chapter=Source Width in Music Production. Methods in Stereo, Ambisonics, and Wave Field Synthesis |doi=10.1007/978-3-319-47292-8_10}}</ref>
==Downmixing==
The mixdown process converts a program with a multiple-channel configuration into a program with fewer channels. Common examples include downmixing from [[5.1 surround sound]] to stereo,{{efn|The left and right surround channels are blended with the left and right front channels. The center channel is blended equally with the left and right channels. The LFE channel is either mixed with the front signals or not used.}} and stereo to mono. Because these are common scenarios, it is common practice to verify the sound of such downmixes during the production process to ensure stereo and mono compatibility.
The alternative channel configuration can be explicitly authored during the production process with multiple channel configurations provided for distribution. For example, on [[DVD-Audio]] or [[Super Audio CD]], a separate stereo mix can be included along with the surround mix.<ref name="Bartlett & Bartlett">{{cite book|last1=Bartlett|first1=Bruce|last2=Bartlett|first2=Jenny|title=Practical Recording Techniques|url=https://archive.org/details/practicalrecordi00bart_029|url-access=limited|date=2009|publisher=Focal Press|location=Oxford, United Kingdom|isbn=978-0-240-81144-4|page=[https://archive.org/details/practicalrecordi00bart_029/page/n643 484]|edition=5th}}</ref> Alternatively, the program can be automatically downmixed by the end consumer's audio system. For example, a [[DVD player]] or [[sound card]] may downmix a [[surround sound]] program to stereo for playback through two speakers.<ref>{{cite web |title=What Is Downmixing? Part 1: Stereo (LoRo) |url=https://www.tvtechnology.com/opinions/what-is-downmixing-part-1-stereo-loro |website=TVTechnology|date=6 March 2007 }}</ref><ref>{{cite web |last1=Thornton |first1=Mike |title=Podcast Follow Up - Surround Mixdown Formats |url=https://www.pro-tools-expert.com/home-page/2012/3/1/podcast-follow-up-surround-mixdown-formats.html |website=Pro Tools Expert|date=March 2012 }}</ref>
==Mixing in surround sound==
Any console with a sufficient number of mix busses can be used to create a [[5.1 surround sound]] mix, but this may be frustrating if the console is not specifically designed to facilitate signal routing, panning, and processing in a [[surround sound]] environment. Whether working in an analog hardware, digital hardware, or [[digital audio workstation|DAW]] mixing environment, the ability to pan mono or stereo sources and place effects in the 5.1 soundscape and monitor multiple output formats without difficulty can make the difference between a successful or compromised mix.<ref name="Huber & Runstein">{{cite book|last1=Huber|first1=David Miles|last2=Runstein|first2=Robert|title=Modern Recording Techniques|url=https://archive.org/details/modernrecordingt00hube_657|url-access=limited|date=2010|publisher=Focal Press|location=Oxford, United Kingdom|isbn=978-0-240-81069-0|page=[https://archive.org/details/modernrecordingt00hube_657/page/n670 559]|edition=7th}}</ref> Mixing in surround is very similar to mixing in stereo except that there are more speakers, placed to ''surround'' the listener. In addition to the horizontal panoramic options available in stereo, mixing in surround lets the [[mix engineer]] pan sources within a much wider and more enveloping environment. In a surround mix, sounds can appear to originate from many more or almost any direction depending on the number of speakers used, their placement and how audio is processed.
There are two common ways to approach mixing in surround. Naturally, these approaches can be combined in any way the [[mix engineer]] sees fit.
*'''Expanded Stereo'''&nbsp;– With this approach, the mix will still sound very much like an ordinary stereo mix. Most of the sources, such as the instruments of a band, backing vocals, and so on, are panned between the left and right speakers.{{efn|Lower levels of these sources may also be sent to the rear speakers in order to create a wider stereo image.}} Lead sources such as the main vocal are sent to the [[center speaker]]. Additionally, reverb and delay effects will often be sent to the rear speakers to create a more realistic sense of being in an acoustic space. For the case of mixing a live recording that was performed in front of an audience, signals recorded by microphones aimed at, or placed among the audience are sent to the rear speakers to make the listener feel as if they are a part of the audience.
*'''Complete Surround/All speakers treated equally'''&nbsp;– Instead of following the traditional ways of mixing in stereo, this much more liberal approach lets the [[mix engineer]] do anything they want. Instruments can appear to originate from anywhere, or even spin around the listener. When done appropriately and with taste, interesting sonic experiences can be achieved.
Recently, a third approach to mixing in surround was developed by surround [[mix engineer]] Unne Liljeblad.
*'''Multi Stereo Surround (MSS)'''<ref name="MMS&nbsp;— Multi Stereo Surround">{{cite web |url=http://www.mix-engineer.com/audio-philosophy/surround-sound-mixing/ |title=Surround Sound Mixing |publisher=www.mix-engineer.com |access-date=2010-01-12 }}</ref>&nbsp;– This approach treats the speakers in a surround sound system as a multitude of stereo pairs. For example, a stereo recording of a piano, created using two microphones in an [[ORTF stereo technique|ORTF configuration]], might have its left channel sent to the left-rear speaker and its right channel sent to the center speaker. The piano might also be sent to a reverb having its left and right outputs sent to the left-front speaker and right-rear speaker, respectively. Thus, multiple clean stereo recordings surround the listener without the smearing comb-filtering effects that often occur when the same or similar sources are sent to multiple speakers.
==Mixing in 3D sound==
An extension to surround sound is 3D sound, used by formats such as [[Dolby Atmos]]. Known as ''object-based'' sound, this enables additional speakers to represent height channels, with as many as 64 unique speaker feeds.<ref>{{cite web|url=https://www.dolby.com/us/en/technologies/home/dolby-atmos.html|title=Dolby Atmos for Home|website=www.dolby.com}}</ref><ref name="engadget">{{cite web|url=https://www.engadget.com/2012/04/26/dolby-atmos-technology-gives-new-meaning-to-surround-sound/|title=Dolby's Atmos technology gives new meaning to surround sound, death from above|publisher=[[Engadget]]|author=Hidalgo, Jason|date=April 26, 2012|access-date=2012-06-01}}</ref> This has application in concert recordings, movies and videogames, and nightclub events.<ref>{{cite book |url=https://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/Authoring_for_Dolby_Atmos_Cinema_Sound_Manual(1).pdf |title=Authoring for Dolby Atmos Cinema Sound Manual |date=2014 |publisher=Dolby Laboratories, Inc. |edition=Third |pages=69–103 |access-date=7 December 2014 |archive-date=10 July 2015 |archive-url=https://web.archive.org/web/20150710150019/http://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/Authoring_for_Dolby_Atmos_Cinema_Sound_Manual(1).pdf |url-status=dead }}</ref>
==See also==
*[[Live sound mixing]]
==Notes==
{{Notelist}}
==References==
{{Reflist}}
==External links==
*[https://modernmixing.com Modern Mixing Mixing Articles and Tutorials]
{{Music production}}
[[Category:Audio mixing| ]]
[[Category:Sound production technology]]
[[Category:Sound recording]]