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{{Short description |Audible impression of a spatially extended sound source}}

{{technical|date=July 2018}}

'''Apparent source width (ASW)''' refers to the perceived "spatial extent" of a sound source. This [[Psychoacoustics|psychoacoustic]] phenomenon is influenced by both the sound radiation pattern of the source itself and the acoustic properties of the environment in which it is located. A wide ASW is often a desirable characteristic, particularly in genres like [[classical music]], [[opera]], and [[historically informed performance]], as it is associated with the immersive sound of acoustic spaces. The study of ASW draws upon research from various fields, including [[room acoustics]], [[architectural acoustics]], [[auralization]], [[musical acoustics]], [[psychoacoustics]], and [[systematic musicology]].

'''Apparent source width (ASW)''' is the audible impression of a spatially extended sound source. Physically, this psychoacoustic impression results from sound radiation characteristics and room acoustical properties. Wide sources are desired by listeners of music. Apparent source width affects the perceived sound of [[acoustic music|unplugged]] [[concert]]s of [[art music]], [[opera]], [[classical music]], [[historically informed performance]] and [[contemporary classical music]], as well as concerts and [[musical theatre]] that use [[live event support]], like [[live sound mixing]], [[sound reinforcement system]]s or a [[public address system]]. Research concerning the ASW comes from the field of [[room acoustics]], [[architectural acoustics]] and [[auralization]] as well as [[musical acoustics]], [[psychoacoustics]] and [[systematic musicology]].

==Physics and perception==

Apparent source width is the aurally perceived extent of a sound source. Sometimes, it is defined as the impression that a source sounds larger than its opticalvisible size.<ref name="blau">{{cite journal |last1=Blau |first1=Matthias |title=Correlation of apparent source width with objective measures in synthetic sound fields |journal=Acta Acustica United with Acustica |date=2004 |volume=90 |issue=4 |page=720 |url=http://www.ingentaconnect.com/content/dav/aaua/2004/00000090/00000004/art00015# |accessdate=31 May 2018}}</ref> The impression results from several auditory cues, which are affected by the sound radiation characteristics of the source itself and by characteristics of the room. Since the term ''apparent source width'' has been used a lot in the field of subjective room acoustics to characterize how the room affects the perception of source size, the term ''perceived source extent'' has been introduced to highlight that the perception results from both the sound source and the room.<ref name="psfs">{{cite book |last1=Ziemer |first1=Tim |title=Psychoacoustic Music Sound Field Synthesis |volume=7 |date=2020 |publisher=Springer |___location=Cham |isbn=978-3-030-23033-3 |doi=10.1007/978-3-030-23033-3 |series=Current Research in Systematic Musicology }}</ref>

The [[auditory system]] has mechanisms that separate the processing of late [[reverberation]] from the processing of direct sound and early [[Reflection (physics)|reflections]], which is referred to as the [[precedence effect]]. While the late reverberation contributes to the [[perception]] of '''{{vanchor|listener envelopment}}''' and reverberance, the direct sound and the early reflections mostly affect [[Sound localization|source localization]], intimacy and the apparent source width.<ref name="beranek">{{cite book|last1=Beranek|first1=Leo Leroy|s2cid=191844675|title=Concert Halls and Opera Houses: Music, Acoustics, and Architecture|date=2004|publisher=Springer|___location=New York|doi=10.1007/978-0-387-21636-2|isbn=978-1-4419-3038-5|edition=Second}}</ref> The balance of early and late arriving sound affects the perceived clarity, warmth and brilliance.

The auditory system does not process all early sounds together to derive a source ___location. In complicated acoustical scenes, the auditory system integrates those parts of sound that share temporal, spectral, and spatial properties into one so-called auditory stream. An auditory stream is the counterpart to a visible [[wikt:object|object]] in [[Gestalt psychology]]. Several auditory streams are segregated from one another. The process of integration and segregation is referred to as [[auditory scene analysis]], and is believed to be the original function of the ear.<ref name="braun">{{cite book |last1=Braun |first1=Christopher B. |last2=Grande |first2=Terry |editor1-last=Webb |editor1-first=Jacqueline F. |editor2-last=Fay |editor2-first=Richard R. |editor3-last=Popper |editor3-first=Arthur N. |title=Fish Bioacoustics |date=2008 |doi=10.1007/978-0-387-73029-5_4 |publisher=Springer |___location=New York |isbn=978-0-387-73029-5 |page=105 |chapter=Evolution of peripheral mechanisms for the enhancement of sound reception}}</ref> Each auditory stream can have its own apparent source width. One auditory stream may contain the direct sound and early reflections of a single musical instrument or a [[musical ensemble]].

A high strength of low frequencies and incoherence of the left and the right ear of one auditory stream, especially of its direct sound and early reflections, increase the apparent source width.<ref name=blau/><ref name=ziemer/><ref name=beranek/> Even in the absence of room acoustical reflections, the pure direct sound of musical instruments already affects the perceived source extent.<ref name="ziemer" /> Unlike a theoretical [[Point source#Sound|monopole source]], musical instruments do not radiate their sound evenly in all directions. Rather, the overall [[Amplitude|volume]] and the [[frequency spectrum]] differ in each direction. This is referred to as sound radiation characteristics or radiation patterns.<ref name=ziemer/><ref name="ziemerdiss" /><ref name="bader" /> These may create incoherent signals at the ears and, consequently, the impression of a wide source. The sound radiation characteristics of musical instruments are typically given as a [[radiation pattern]] in a two- or three-dimensional [[polar coordinate system]].<ref name="meyer" /><ref name="patynen" /><ref name="ziemerj" /><ref name="zotter" />

Even in absence of room acoustical reflections the pure direct sound of musical instruments already effects the perceived source extent.<ref name="ziemer">{{cite book|last1=Ziemer|first1=Tim|editor1-last=Schneider|editor1-first=Albrecht|title=Studies in Musical Acoustics and Psychoacoustics|volume=4|doi=10.1007/978-3-319-47292-8_10|date=2017|publisher=Springer|___location=Cham|isbn=978-3-319-47292-8|pages=299–340|chapter=Source Width in Music Production. Methods in Stereo, Ambisonics, and Wave Field Synthesis|series=Current Research in Systematic Musicology}}</ref> Unlike hypothetical [[Point source#Sound|monopole source]] musical instruments radiate their sound not evenly in all directions. Rather the overall [[Amplitude|volume]] and the [[frequency spectrum]] differ in each direction, referred to as sound radiation characteristics or radiation patterns.<ref name=ziemer/><ref name="ziemerdiss">{{cite thesis|type=PhD|doi=10.13140/RG.2.1.1997.9769|last1=Ziemer|first1=Tim|title=Implementation of the Radiation Characteristics of Musical Instruments in Wave Field Synthesis Applications|date=2015|publisher=Univ. Diss.|___location=Hamburg|url=https://ediss.sub.uni-hamburg.de/volltexte/2016/7939/|accessdate=25 May 2018}}</ref><ref name="bader">{{cite journal|last1=Bader|first1=Rolf|title=Radiation characteristics of multiple and single sound hole vihuelas and a classical guitar|journal=The Journal of the Acoustical Society of America|date=2012|volume=131|issue=1|pages=819–828|doi=10.1121/1.3651096|pmid=22280704|bibcode=2012ASAJ..131..819B}}</ref> These may create incoherent ear signals and, consequently, the impression of a wide source. The sound radiation characteristics of musical instruments are typically given as [[radiation pattern]] in a two- to three-dimensional [[polar coordinate system]].<ref name="meyer">{{cite book|last1=Meyer|first1=Jürgen|doi=10.1007/978-0-387-09517-2|title=Acoustics and the Performance of Music. Manual for Acousticians, Audio Engineers, Musicians, Architects and Musical Instrument Makers|date=2009|publisher=Springer|___location=Bergkirchen|isbn=978-0-387-09516-5|edition=Fifth |url=http://cds.cern.ch/record/1339014}}</ref><ref name="patynen">{{cite journal|last1=Pätynen|first1=Jukka|last2=Lokki|first2=Tapio|s2cid=119661613|title=Directivities of Symphony Orchestra Instruments|journal=Acta Acustica United with Acustica|date=2010|volume=96|issue=1|pages=138–167|doi=10.3813/aaa.918265}}</ref><ref name="ziemerj">{{cite journal|last1=Ziemer|first1=Tim|last2=Bader|first2=Rolf|title=Psychoacoustic Sound Field Synthesis for Musical Instrument Radiation Characteristics|journal=Journal of the Audio Engineering Society|date=2017|volume=65|issue=6|pages=482–496|doi=10.17743/jaes.2017.0014}}</ref><ref name="zotter">{{cite thesis|type=PhD||institution=University of Music and Performing Arts Graz|last1=Zotter|first1=Franz|title=Analysis and Synthesis of Sound-Radiation with Spherical Arrays|date=2009|___location=Graz|url=https://iem.kug.ac.at/en/projects/workspace/projekte-bis-2008/dsp/analysis-and-synthesis-of-sound-radiation-with-spherical-arrays.html|accessdate=25 May 2018}}</ref>

==Subjective room acoustics==

The apparent source width and other subjective sound properties in many concert halls have been rated by experts, likeincluding [[Conducting|conductorconductors]]s and [[Music criticism|music criticscritic]]s. Together, apparent source width and listener envelopment are the most important contributors to the spaciousness impression of a concert hall, which is the most important contributor to the quality ratings of concert halls.<ref name=beranek />

In the field of subjective [[room acoustics]], the sound radiation characteristics are ignored and the apparent source width is explained by means of objective measures of room [[impulse response]]s, like the binaural quality index, the lateral energy fraction and the early sound strength.<ref name=beranek /><ref name=ziemer /><ref name=blau /> These tend to correlate with the subjective expert ratings. Accordingly, early, incoherent, lateral reflections, together with a high [[loudness]] of low frequencies in the early reflections of the room reverberation, increase the apparent source width and thus the overall spaciousness and quality of a concert hall. This knowledge is used in [[architectural acoustics]] to design a concert hallhalls that exhibitsexhibit the desired acoustical properties.

==Music production==

In [[audio mastering]] and [[sound recording and reproduction]], a major task of the [[recording studio]]`s [[audio engineer]]s and [[record producer]]s is to make musical instruments sound huge.<ref name="huge">{{cite book|last1=Levinit|first1=D.J.|editor1-last=Greenbaum|editor1-first=K.|editor2-last=Barzel|editor2-first=R.|title=Audio Anecdotes|publisher=A K Peters|___location=Natick|volume=vol. I|isbn=978-1568811048|pages=147–158|chapter=Instrument (and vocal) recording tips and tricks|date=2004-03-11}}</ref> The increase of apparent source width is as important as [[Equalization (audio)|spectral balancing]] and [[dynamic range compression]].<ref name="mastering">{{cite book|last1=Kaiser|first1=C.|title=1001 Mastering Tipps|date=2013|publisher=mitp|___location=Heidelberg|page=23,40}}</ref>

This is can be achieved with established recording techniques, like [[Microphone practice#A-B technique: time-of-arrival stereophony|A-B technique]], [[Blumlein pair|Blumlein technique]], [[Microphone practice#M/S technique: Mid/Side stereophony|M-S technique]], and the [[ORTF stereo technique]], [[Microphone practice#X-Y technique: intensity stereophony|X-Y technique]], or by experimenting with different types of microphones and microphone locations, like [[Microphone#Dynamic|dynamic microphones]], [[Microphone#Ribbon|ribbon microphones]], [[Microphone#contact microphone|contact microphones]], [[boundary microphone]]s and [[Microphone#Speakers as microphones|loudspeakers as microphones]].

Signals that sound too narrow — like too coherent stereo recordings, monophonic recordings or synthetic sounds — can be widened by so-called pseudostereophony.<ref name="csound">{{cite journal|last1=Cabrera|first1=Andrés|editor1-last=Hearon|editor1-first=James|editor2-last=Yi|editor2-first=Steven|title=Pseudo-stereo Techniques|journal=CSound Journal|date=2011|issue=14|url=http://csoundjournal.com/issue14/PseudoStereo.html|accessdate=25 May 2018}}</ref><ref name="faller">{{cite conference|last1=Faller|first1=Christoph|title=Pseudostereophony Revisited|conference=Audio Engineering Society Convention 118|pages=paper number 6477|date=2005|url=http://www.aes.org/e-lib/browse.cfm?elib=13193|accessdate=25 May 2018}}</ref><ref name=ziemer/> These techniques have in common that they [[decorrelation|decorrelate]] the stereo channels by applying individual [[audio filter]]s, [[Reverberation#Creating reverberation effects|reverberation]] andor [[Delay (audio effect)|delay effects]] to each. ThisThe way the tworesulting channels' signals are similar enough to be heard as one integrated stream, i.e., one auditory sound object., At the same time the signalsbut are so diverse that they do not seem to originate infrom a tiny [[point source]] but rather infrom a broad source. Such techniques were also used in [[Duophonic]] sound to re-release monophonic recordings with pseudo-stereophonic sound.

Such techniques were also used in [[Duophonic]] sound to re-release monophonic recording with pseudo-stereophonic sound.

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A "surround" sound section could be added to discuss asw in mono/stereo/Dolby Surround/Quadraphonic Sound/5.1/auro3D/Dolby Atmos/Ambisonics/Wave Field Synthesis...:

==Surround Sound==

[[monaural]]

[[stereophonic sound]]

[[quadraphonic sound]]

[[Dolby Pro Logic]]

[[5.1 surround sound]]

[[Dolby Atmos]]

[[Auro-3D]]

[[ambisonics]]

[[wave field synthesis]]

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==Related sound impressions==

Several subjective sound impressions are closely related to apparent source width. Reverberance refers to the impression that spatially and temporally distributed sounds blend due to reverberation. [[Liveness]] is the impression that the room contributes more than just repetitions of direct sound. A live concert sounds better in a reverberant hall than in a dead or dry hall. In intimate halls, instruments sound nearclose to the listener and the hall sounds small. Listener envelopment is the impression that the listener takes ais bathbathed in sound, i.e., that the sound comes from all over the placedirections. Spaciousness is a term that summarizes apparent source width and listener envelopment.<ref name=beranek/>

==References==

{{Reflist}}|refs=

<ref name="csound">{{cite journal |last1=Cabrera |first1=Andrés |editor1-last=Hearon |editor1-first=James |editor2-last=Yi|editor2-first=Steven |title=Pseudo-stereo Techniques |journal=CSound Journal |date=2011 |issue=14 |url=http://csoundjournal.com/issue14/PseudoStereo.html |access-date=25 May 2018}}

</ref>

<ref name="faller">{{cite conference |last1=Faller |first1=Christoph |title=Pseudostereophony Revisited|conference=Audio Engineering Society Convention 118 |pages=Paper Number 6477 |date=2005 |url=http://www.aes.org/e-lib/browse.cfm?elib=13193 |access-date=25 May 2018}}</ref>

<ref name="huge">{{cite book |last1=Levinit |first1=D.J. |editor1-last=Greenbaum |editor1-first=K. |editor2-last=Barzel |editor2-first=R. |title=Audio Anecdotes |publisher=A K Peters |___location=Natick |volume=I |isbn=978-1568811048 |pages=147–158 |chapter=Instrument (and vocal) recording tips and tricks |date=2004-03-11}}</ref>

<ref name="mastering">{{cite book |last1=Kaiser |first1=C. |title=1001 Mastering Tipps |date=2013 |publisher=mitp |___location=Heidelberg |page=23,40}}</ref>

<ref name="blau">{{cite journal |last1=Blau |first1=Matthias |title=Correlation of apparent source width with objective measures in synthetic sound fields |journal=Acta Acustica United with Acustica |date=2004 |volume=90 |issue=4 |page=720 |url=http://www.ingentaconnect.com/content/dav/aaua/2004/00000090/00000004/art00015# |accessdate=31 May 2018}}</ref>

<ref name="braun">{{cite book |last1=Braun |first1=Christopher B. |last2=Grande |first2=Terry |editor1-last=Webb |editor1-first=Jacqueline F. |editor2-last=Fay |editor2-first=Richard R. |editor3-last=Popper |editor3-first=Arthur N. |title=Fish Bioacoustics |date=2008 |doi=10.1007/978-0-387-73029-5_4 |publisher=Springer |___location=New York |isbn=978-0-387-73029-5 |page=105 |chapter=Evolution of peripheral mechanisms for the enhancement of sound reception}}</ref>

<ref name="psfs">{{cite book |last1=Ziemer |first1=Tim |title=Psychoacoustic Music Sound Field Synthesis |volume=7 |date=2020 |publisher=Springer |___location=Cham |isbn=978-3-030-23033-3 |doi=10.1007/978-3-030-23033-3 |series=Current Research in Systematic Musicology |s2cid=201136171 }}</ref>

<ref name="beranek">{{cite book |last1=Beranek |first1=Leo Leroy |s2cid=191844675 |title=Concert Halls and Opera Houses: Music, Acoustics, and Architecture |date=2004 |publisher=Springer |___location=New York |doi=10.1007/978-0-387-21636-2 |isbn=978-1-4419-3038-5 |edition=Second}}</ref>

<ref name="ziemer">{{cite book |last1=Ziemer |first1=Tim |editor1-last=Schneider |editor1-first=Albrecht |title=Studies in Musical Acoustics and Psychoacoustics |volume=4 |doi=10.1007/978-3-319-47292-8_10 |date=2017 |publisher=Springer |___location=Cham |isbn=978-3-319-47292-8 |pages=299–340 |chapter=Source Width in Music Production. Methods in Stereo, Ambisonics, and Wave Field Synthesis |series=Current Research in Systematic Musicology}}</ref>

<ref name="ziemerdiss">{{cite thesis |type=PhD |doi=10.13140/RG.2.1.1997.9769 |last1=Ziemer |first1=Tim |title=Implementation of the Radiation Characteristics of Musical Instruments in Wave Field Synthesis Applications |date=2015 |publisher=Univ. Diss. |___location=Hamburg |url=https://ediss.sub.uni-hamburg.de/volltexte/2016/7939/ |accessdate=25 May 2018}}</ref>

<ref name="bader">{{cite journal |last1=Bader |first1=Rolf |title=Radiation characteristics of multiple and single sound hole vihuelas and a classical guitar |journal=The Journal of the Acoustical Society of America |date=2012 |volume=131 |issue=1 |pages=819–828 |doi=10.1121/1.3651096 |pmid=22280704 |bibcode=2012ASAJ..131..819B}}</ref>

<ref name="meyer">{{cite book |last1=Meyer |first1=Jürgen |doi=10.1007/978-0-387-09517-2 |title=Acoustics and the Performance of Music. Manual for Acousticians, Audio Engineers, Musicians, Architects and Musical Instrument Makers |date=2009 |publisher=Springer |___location=Bergkirchen |isbn=978-0-387-09516-5 |s2cid=60810170 |edition=Fifth |url=https://cds.cern.ch/record/1339014}}</ref>

<ref name="patynen">{{cite journal |last1=Pätynen |first1=Jukka |last2=Lokki |first2=Tapio |s2cid=119661613 |title=Directivities of Symphony Orchestra Instruments |journal=Acta Acustica United with Acustica |date=2010 |volume=96 |issue=1 |pages=138–167 |doi=10.3813/aaa.918265}}</ref>

<ref name="ziemerj">{{cite journal |last1=Ziemer |first1=Tim |last2=Bader |first2=Rolf |title=Psychoacoustic Sound Field Synthesis for Musical Instrument Radiation Characteristics |journal=Journal of the Audio Engineering Society |date=2017 |volume=65 |issue=6 |pages=482–496 |doi=10.17743/jaes.2017.0014}}</ref>

<ref name="zotter">{{cite thesis |type=PhD |institution=University of Music and Performing Arts Graz |last1=Zotter |first1=Franz |title=Analysis and Synthesis of Sound-Radiation with Spherical Arrays |date=2009 |___location=Graz |url=https://iem.kug.ac.at/en/projects/workspace/projekte-bis-2008/dsp/analysis-and-synthesis-of-sound-radiation-with-spherical-arrays.html |accessdate=25 May 2018}}</ref>

}}

[[Category:Psychoacoustics]]