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{{Short description|Audio programming language}}
{{redirect|FAUST|other uses|Faust (disambiguation){{!}}Faust}}
{{More footnotes needed|date=March 2015}}
{{Infobox software
| name = FAUST
| developer = GRAME, Centre National de Création Musicale
| author = Yann Orlarey, Dominique Fober, Stéphane Letz
| released = {{releasestart date|2002}}
| latest release version = 2.560.233<ref>[https://github.com/grame-cncm/faust/releases Releases · grame-cncm/faust · GitHub]</ref>
| latest release date = {{releasestart date|20182023|0306|0614}}
| operating system = [[Linux]], [[OS X]], [[Microsoft Windows|Windows]], [[Unix]]
| genre = Functional programming language for audio signal processing
| repo = {{URL|https://github.com/grame-cncm/faust/}}
| programming language = [[C++]]
| license = [[GNU General Public License|GPL]]
| website = {{URL|faust.grame.fr}}
}}
{{Portal|Free and open-source software}}
 
'''FAUST''' (Functional AUdio STream) is a [[Domain ___domain-specific language|___domain-specific]] [[Purelypurely functional programming|purely functional]] [[programming language]] for implementing [[signal processing]] [[algorithms]] in the form of [[Library (computing)|libraries]], [[audio plug-ins]], or standalone applications. A FAUST program denotes a signal processor: a mathematical function that is applied to some input signal and then fed out.
 
==Overview==
The FAUST [[programming model]] combines a [[functional programming]] approach with a [[block diagram]] syntax:
* The functional programming approach provides a natural framework for [[signal processing]]. Digital signals are modeled as [[Sequence|discrete functions]] of time, signal processors as [[Higher-order function|second order functions]] that operate on them, and FAUST’sFAUST's block diagram ''composition operators'', used to combine signal processors together, as third order functions, etc.
* Block diagrams, even if purely textual as in FAUST, promote a modular approach to signal processing that complies with sound engineers' and audio developers' habits.
A FAUST program doesn’tdoesn't describe a sound or a group of sounds, but a [[Digital signal processing|signal processor]]. The program source is organized as a set of ''definitions'' with at least the definition of the keyword <code>process</code> (the equivalent of <code>main</code> in C):
<sourcesyntaxhighlight lang=haskell>
process = ...;
</syntaxhighlight>
</source>
 
The FAUST [[compiler]] translates FAUST code into a [[C++]] [[Object-oriented programming|object]], which may then interface with other C++ code to produce a full program.
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==Example code==
FAUST programs define a <code>process</code> function that operates on incoming data. This is analogous to the <code>main</code> function in most programming languages. The following is an example that produces silence:
<sourcesyntaxhighlight lang="haskell">
process = 0;
</syntaxhighlight>
</source>
The second example copies the input signal to the output. It involves the <code>_</code> primitive that denotes the [[identity function]] for signals:
<sourcesyntaxhighlight lang="haskell">
process = _;
</syntaxhighlight>
</source>
Another example sums a stereo signal into a mono signal using the <code>+</code> primitive:
<sourcesyntaxhighlight lang="haskell">
process = +;
</syntaxhighlight>
</source>
[[File:Faust-simple-block-diagram.jpg|thumb|Block diagrams generated by Faust from some simple programs]]
Most FAUST primitives are analogous to their C counterpart on numbers, but lifted to signals. For example, the FAUST primitive <code>sin</code> operates on a signal X by applying the [[C (programming language)|C]] function <code>sin</code> to each sample X[t]. All C numerical functions have their counterpart in FAUST.
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Using the sequential composition operator <code>:</code> the output of <code>+</code> can be routed to the input of <code>abs</code> to compute the [[absolute value]] of the signal:
<sourcesyntaxhighlight lang="haskell">
process = + : abs;
</syntaxhighlight>
</source>
Here is an example of parallel composition using the <code>,</code> operator that arranges its left and right expressions in parallel. This is analogous to a stereo cable.
<sourcesyntaxhighlight lang="haskell">
process = _,_;
</syntaxhighlight>
</source>
These operators can be arbitrarily combined arbitrarily. The following code multiplies an input signal with 0.5:
<sourcesyntaxhighlight lang="haskell">
process = _,0.5 : *;
</syntaxhighlight>
</source>
The above may be rewritten in [[currying|curried]] form:
<sourcesyntaxhighlight lang="haskell">
process = *(0.5);
</syntaxhighlight>
</source>
The recursive composition operator <code>~</code> can be used to create block diagrams with cycles (that include an implicit one-sample delay). Here is an example of an integrator that takes an input signal X and computes an output signal Y such that Y(t) = X(t) + Y(t−1):
<sourcesyntaxhighlight lang=haskell>
process = + ~ _;
</syntaxhighlight>
</source>
 
==Generating full applications==
Using specific ''architecture files'', a FAUST program can be used to produce code for a variety of platforms and plug-in formats. These architecture files act as wrappers and describe the interactions with the host audio and GUI system. {{As of|20152021}}, more than 1030 architectures are supported and new ones may be implemented by anyone.
 
[[File:Faust-mixer-jackqt.jpg|thumb|Screenshot of mixer.dsp (available in the FAUST distribution) using the jack-qt architecture]]
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{| class="wikitable"
|+ Some architecture files available for FAUST
! File
| alsa-gtk.cpp || ALSA application + GTK▼
! Architecture
|-
| alsa-qtgtk.cpp || ALSA application + QT4[[GTK]]
|-
▲| alsa-gtkqt.cpp || ALSA application + GTK[[Qt (software)|Qt]] 4
|-
| android.cpp || Android applications
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| au.cpp || Audio Unit plug-in
|-
| ca-qt.cpp || CoreAudio application + QT4Qt 4
|-
| ios-coreaudio.cpp || iPhone and iPad applications
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| jack-gtk.cpp || JACK application + GTK
|-
| jack-qt.cpp || JACK application + QT4Qt 4
|-
| ladspa.cpp || LADSPA plug-in
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| max-msp.cpp || Max MSP plug-in
|-
| pd.cpp || PuredataPure Data plug-in
|-
| q.cpp || Q language plug-in
|-
| supercollider.cpp || SupercolliderSuperCollider plug-in
|-
| vst.cpp || VST plug-in
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A useful option makes it possible to generate the block diagram representation of the program as one or more SVG graphic files.
 
It is useful to note the difference between the block diagram and the generated C++ code. As stated, the key idea here is not to compile the block diagram literally, but the mathematical function it denotes. Modern C/C++ compilers also don’tdon't compile programs literally. But because of the complex semantics of C/C++ (due to side effects, pointer aliasing, etc.) they can’tcan't go very far in that direction. This is a distinct advantage of a purely functional language: it allows compilers to do very advanced optimisations.
 
==Arrows-like semantics==
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{| class="wikitable"
|+ Equivalences between FAUST and Arrow combinators
| <code>f~g</code> || <{{code>|2=haskell|1=loop ((\(a,b) -> (b,a)) ^>> f >>> id &&& (delay>>>g))</code>}} where <code>delay</code> is not a method of the <code>Arrow</code> type class, but is specific to signal processing arrows
|-
| <code>f,g</code> || <code>f***g</code>
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| year = 2011
}}
* {{cite journal
|first1=Pierre
|last1=Jouvelot
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|url=http://faust.grame.fr/images/faust-doc/papers/faust-elsevier2011.pdf
|year=2011
|volume=37
}}{{dead link|date=December 2016 |bot=InternetArchiveBot |fix-attempted=yes }}▼
|issue=3
|pages=113–131
|doi=10.1016/j.cl.2011.03.001
▲ }}{{dead link|date=December 2016 |bot=InternetArchiveBot |fix-attempted=yes }}
* {{Cite web
| first = Julius O.
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| year = 2011
}}
* {{cite journal
|first3=Dominique
|last3=Fober
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|url=http://faust.grame.fr/images/faust-doc/papers/faust-CFA-2010.pdf
|year=2010
}}{{dead link|date=December 2016 |bot=InternetArchiveBot |fix-attempted=yes }}
* {{cite journal
| first3 = Dominique
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| year = 2010
}}
* {{cite journal
|first1=Jérôme
|last1=Barthélemy
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|pages=369–372
|year=2010
}}{{dead link|date=December 2016 |bot=InternetArchiveBot |fix-attempted=yes }}
* {{cite journal
| first1 = Pierre
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| archive-url = https://web.archive.org/web/20120407043121/http://smcnetwork.org/files/proceedings/2010/51.pdf
| archive-date = 2012-04-07
| dead-url-status = yesdead
}}
* {{cite journal
|first3=Dominique
|last3=Fober
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|url=http://faust.grame.fr/test/images/faust-doc/papers/faustLAC09.pdf
|year=2009
}}{{dead link|date=December 2016 |bot=InternetArchiveBot |fix-attempted=yes }}
* {{cite book
| first1 = Pierre
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| url = http://faust.grame.fr/images/faust-doc/papers/multirate-faust.pdf
| year = 2009
}}{{Dead link|date=December 2019 |bot=InternetArchiveBot |fix-attempted=yes }}
}}
* {{cite journal
| first2 = Dominique
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| url = http://smc2009.smcnetwork.org/programme/pdfs/232.pdf
| year = 2009
| archive-date = 2012-04-25
| access-date = 2011-10-11
| archive-url = https://web.archive.org/web/20120425061241/http://smc2009.smcnetwork.org/programme/pdfs/232.pdf
| url-status = dead
}}
* {{cite book
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| isbn = 978-2-7521-0054-2
| year = 2009
}}{{Dead link|date=December 2019 |bot=InternetArchiveBot |fix-attempted=yes }}
}}
* {{cite journal
|first3=Dominique
|last3=Fober
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|url=http://faust.grame.fr/images/faust-doc/papers/jack-faust-multicore.pdf
|year=2008
}}{{dead link|date=December 2016 |bot=InternetArchiveBot |fix-attempted=yes }}
* {{cite journal
| first = Albert
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| last = Smith III
| title = Introduction to Digital Filters: With Audio Applications
| chapter = Appendix K. Digital Filtering in Faust and PD
| publisher = W3K Publishing
| year = 2007
| isbn = 978-0-9745607-1-7
| chapter-url = https://books.google.com/books?id=pC1iCQUAsHEC&pg=PA417
| pages = 417-417–?
}}
* {{cite journal
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| publisher = Computer Music Association
| url = http://quod.lib.umich.edu/cgi/t/text/text-idx?c=icmc;idno=bbp2372.2005.*
| chapterurlchapter-url = http://quod.lib.umich.edu/i/icmc/bbp2372.2005.054?view=image
| year = 2005
| page = 286
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| url = http://faust.grame.fr/images/faust-doc/papers/faust-soft-computing.pdf
| year = 2004
}}{{Dead link|date=December 2019 |bot=InternetArchiveBot |fix-attempted=yes }}
}}
* {{cite journal
|first1=Nicolas
|last1=Scaringella
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|url=http://faust.grame.fr/images/faust-doc/papers/JIM2003vect.pdf
|year=2003
}}{{dead link|date=December 2016 |bot=InternetArchiveBot |fix-attempted=yes }}
* {{cite journal
|first3=Stéphane
|last3=Letz
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|url=http://faust.grame.fr/images/faust-doc/papers/faust-jim2002.pdf
|year=2002
}}{{dead link|date=December 2016 |bot=InternetArchiveBot |fix-attempted=yes }}
* {{cite journal
|first3=Stéphane
|last3=Letz
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|url=http://faust.grame.fr/images/faust-doc/papers/faust-icmc2002.pdf
|year=2002
}}{{dead link|date=December 2016 |bot=InternetArchiveBot |fix-attempted=yes }}
{{Refend}}
 
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{{Commons category|FAUST (programming language)}}
* {{Official website|faust.grame.fr}}, online compiler, support, documentation, news, etc.
* {{GitHub|grame-cncm/faust}}
 
[[Category:Audio programming languages]]
[[Category:Programming languages created in 2002]]
Retrieved from "https://en.wikipedia.org/wiki/FAUST_(programming_language)"