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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 = {{start date|2002}}
| latest release version = 2.60.3<ref>[https://github.com/grame-cncm/faust/releases Releases · grame-cncm/faust · GitHub]</ref>
| latest release date = {{start date|2023|06|14}}
| 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-specific language|___domain-specific]] [[purely 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'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'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):
<syntaxhighlight lang=haskell>
process = ...;
</syntaxhighlight>
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.
The generated code works at the sample level. It is therefore suited to implement low-level [[Digital signal processing|DSP]] functions like [[Infinite impulse response|recursive filters]]. The code may also be [[Embedded software|embedded]]. It is self-contained and does not depend on any DSP library or [[runtime system]]. It has a very deterministic behavior and a constant memory size.
The semantics of FAUST is driven to be simple and well-defined. It allows the FAUST compiler to be ''semantically driven''. Instead of compiling a program literally, it compiles the mathematical function it denotes. This may promote component reuse. Moreover, having access to the exact semantics of a FAUST program can simplify preservation issues.
FAUST is a textual language but block diagram oriented. It combines two approaches: [[functional programming]] and algebraic [[block diagram]]s, which are constructed via [[function composition]]. For that, FAUST relies on a ''block diagram algebra'' of five composition operations.
==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:
<syntaxhighlight lang="haskell">
process = 0;
</syntaxhighlight>
The second example copies the input signal to the output. It involves the <code>_</code> primitive that denotes the [[identity function]] for signals:
<syntaxhighlight lang="haskell">
process = _;
</syntaxhighlight>
Another example sums a stereo signal into a mono signal using the <code>+</code> primitive:
<syntaxhighlight lang="haskell">
process = +;
</syntaxhighlight>
[[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.
Some [[signal processing]] primitives are specific to FAUST. For example, the delay operator <code>@</code> takes two input signals: X (the signal to be delayed) and D (the delay to be applied), and produces an output signal Y such that Y(t) = X(t − D(t)).
==Block diagram composition==
Contrary to [[Max (software)|Max-like]] [[visual programming languages]] where the user does manual connections, FAUST primitives are assembled in [[block diagram]]s by using a set of high-level block diagram [[Function composition|composition]] operations.
[[File:Faust-simple-block-diagrams.jpg|thumb|upright=1.75|Simple examples of block diagram composition]]
{| class="wikitable"
|+ The block diagram ''composition operators'' used in FAUST
| f~g || Recursive composition (precedence 4)
|-
| f,g || Parallel composition (precedence 3)
|-
| f:g || Sequential composition (precedence 2)
|-
| f<:g || Split composition (precedence 1)
|-
| f:>g || Merge composition (precedence 1)
|}
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:
<syntaxhighlight lang="haskell">
process = + : abs;
</syntaxhighlight>
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.
<syntaxhighlight lang="haskell">
process = _,_;
</syntaxhighlight>
These operators can be combined arbitrarily. The following code multiplies an input signal with 0.5:
<syntaxhighlight lang="haskell">
process = _,0.5 : *;
</syntaxhighlight>
The above may be rewritten in [[currying|curried]] form:
<syntaxhighlight lang="haskell">
process = *(0.5);
</syntaxhighlight>
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):
<syntaxhighlight lang=haskell>
process = + ~ _;
</syntaxhighlight>
==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|2021}}, more than 30 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]]
{| class="wikitable"
|+ Some architecture files available for FAUST
! File
! Architecture
|-
| alsa-gtk.cpp || ALSA application + [[GTK]]
|-
| alsa-qt.cpp || ALSA application + [[Qt (software)|Qt]] 4
|-
| android.cpp || Android applications
|-
| au.cpp || Audio Unit plug-in
|-
| ca-qt.cpp || CoreAudio application + Qt 4
|-
| ios-coreaudio.cpp || iPhone and iPad applications
|-
| jack-gtk.cpp || JACK application + GTK
|-
| jack-qt.cpp || JACK application + Qt 4
|-
| ladspa.cpp || LADSPA plug-in
|-
| max-msp.cpp || Max MSP plug-in
|-
| pd.cpp || Pure Data plug-in
|-
| q.cpp || Q language plug-in
|-
| supercollider.cpp || SuperCollider plug-in
|-
| vst.cpp || VST plug-in
|-
| vsti-mono.cpp || Monophonic VST Instrument plug-in
|-
| vsti-poly.cpp || Polyphonic VST Instrument plug-in
|}
==Generating block diagrams==
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't compile programs literally. But because of the complex semantics of C/C++ (due to side effects, pointer aliasing, etc.) they can'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==
The Faust semantics is almost the same as that of [[Haskell (programming language)|Haskell's]] [[Arrow (computer science)|Arrows]] type class.
However, the Arrow type class is not bound to signal processors.
{| 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))}} 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>
|-
| <code>f:g</code> || <code>f>>>g</code>
|-
| <code>f<:g</code> || <code>f>>^h>>>g</code> with appropriate function <code>h</code> (or <code>&&&</code> in special cases)
|-
| <code>f:>g</code> || <code>f>>^h>>>g</code> with appropriate function <code>h</code>
|}
The Arrow combinators are more restrictive than their FAUST counterparts, e.g., the nesting of parallel composition is preserved, and inputs of the operands of <code>&&&</code> must match exactly.
==References==
{{Reflist}}
{{Refbegin}}
* {{cite journal
|
|
| first2 = Julius O. III
| last2 = Smith
| title = Faust-STK: a Set of Linear and Nonlinear Physical Models for the Faust Programming Language
| journal = Proceedings of the 11th Int. Conference on Digital Audio Effects (DAFx-11)
| url = http://recherche.ircam.fr/pub/dafx11/Papers/20_e.pdf
|
| year = 2011
}}
* {{cite journal
| first1 = Dominique
| last1 = Fober
| first2 = Yann
| last2 = Orlarey
| first3 = Stéphane
| last3 = Letz
| title = Faust Architectures Design and OSC Support
| journal = Proceedings of the 11th Int. Conference on Digital Audio Effects (DAFx-11)
| url = http://recherche.ircam.fr/pub/dafx11/Papers/29_e.pdf
| pages = 213–216
| year = 2011
}}
* {{cite journal
| first1 = Julius O. III
| last1 = Smith
| first2 = Romain
| last2 = Michon
| title = Nonlinear Allpass Ladder Filters in Faust
| journal = Proceedings of the 11th Int. Conference on Digital Audio Effects (DAFx-11)
| url = http://recherche.ircam.fr/pub/dafx11/Papers/38_e.pdf
| pages = 361–364
| year = 2011
}}
* {{cite journal
|first1=Pierre
|last1=Jouvelot
|first2=Yann
|last2=Orlarey
|title=Dependent Vector Types for Data Structuring in Multirate Faust
|journal=Computer Languages, Systems & Structures
|url=http://faust.grame.fr/images/faust-doc/papers/faust-elsevier2011.pdf
|year=2011
|volume=37
|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.
| last = Smith III
| title = Audio Signal Processing in Faust
| url = https://ccrma.stanford.edu/~jos/spf/aspf.pdf
| year = 2011
}}
* {{cite journal
|first3=Dominique
|last3=Fober
|first1=Yann
|last1=Orlarey
|first2=Stéphane
|last2=Letz
|title=Automatic Parallelization of Audio Applications with Faust
|journal=Proceedings of the Congrès Français d'Acoustique
|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
| last3 = Fober
| first2 = Yann
| last2 = Orlarey
| first1 = Stéphane
| last1 = Letz
| title = Work Stealing Scheduler for Automatic Parallelization in Faust
| journal = Proceedings of the Linux Audio Conference (LAC-2010)
| url = http://lac.linuxaudio.org/2010/papers/17.pdf
| year = 2010
}}
* {{cite journal
| first = Albert
| last = Gräf
| title = Term rewriting extension for the Faust programming language
| journal = Proceedings of the 8th International Linux Audio Conference (
| url = http://lac.linuxaudio.org/2010/download/lac2010proceedings.pdf
| page = 117
| year = 2010
}}
* {{cite journal
|first1=Jérôme
|last1=Barthélemy
|first2=Alain
|last2=Bonardi
|first3=Yann
|last3=Orlarey
|first4=Serge
|last4=Lemouton
|first5=Raffaele
|last5=Ciavarella
|first6=Karim
|last6=Barkati
|title=First Steps Towards an Organology of Virtual Instruments in Computer Music
|journal=Proceedings of the 2010 International Computer Music Conference (ICMA-2010)
|url=http://faust.grame.fr/images/faust-doc/papers/astree-icmc2010.pdf
|pages=369–372
|year=2010
}}{{dead link|date=December 2016 |bot=InternetArchiveBot |fix-attempted=yes }}
* {{cite journal
| first1 = Pierre
| last1 = Jouvelot
| first2 = Yann
| last2 = Orlarey
| title = Depandant Vector Types for Multirate Faust
| journal = Proceedings of the 7th Sound and Music Computing Conference (SMC-2010)
| url = http://smcnetwork.org/files/proceedings/2010/51.pdf
| pages = 345–352
| year = 2010
| access-date = 2011-10-11
| archive-url = https://web.archive.org/web/20120407043121/http://smcnetwork.org/files/proceedings/2010/51.pdf
| archive-date = 2012-04-07
| url-status = dead
}}
* {{cite journal
|first3=Dominique
|last3=Fober
|first1=Yann
|last1=Orlarey
|first2=Stéphane
|last2=Letz
|title=Adding Automatic Parallelization to Faust
|journal=Proceedings of the Linux Audio Conference (LAC-2009)
|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
| last1 = Jouvelot
| first2 = Yann
| last2 = Orlarey
| chapter = Semantics for Multirate Faust
| title = Technical Repports of Centre de Recherche en Informatique de MINES ParisTech
| 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
| last2 = Fober
| first1 = Yann
| last1 = Orlarey
| first3 = Stéphane
| last3 = Letz
| title = Parallelization of Audio Applications with Faust
| 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
| first2 = Dominique
| last2 = Fober
| first1 = Yann
| last1 = Orlarey
| first3 = Stéphane
| last3 = Letz
| chapter = Faust: an Efficient Functional Approach to DSP Programming
| title = New Computanionals Paradigms for Computer Music
| url = http://faust.grame.fr/images/faust-doc/papers/faust-delatour2009.pdf
| publisher = Edition Delatour
| isbn = 978-2-7521-0054-2
| year = 2009
}}{{Dead link|date=December 2019 |bot=InternetArchiveBot |fix-attempted=yes }}
* {{cite journal
|first3=Dominique
|last3=Fober
|first1=Yann
|last1=Orlarey
|first2=Stéphane
|last2=Letz
|title=Multicore Technologies in Jack and Faust
|journal=Proceedings of the 2010 International Computer Music Conference (ICMC-2008)
|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
| last = Gräf
| title = Interfacing Pure Data with Faust
| journal = Proceedings of the 5th International Linux Audio Conference (LAC2007)
| url = http://lac.linuxaudio.org/2007/download/lac07_proceedings.pdf
| page = 24
| year = 2007
}}
* {{Cite book
| first =
| last =
| title = Introduction to Digital Filters: With Audio Applications
| chapter = Appendix K. Digital Filtering in Faust and PD
| publisher
| year = 2007
| isbn = 978-0-9745607-1-7
| chapter-url =
| pages = 417–?
}}
* {{cite journal
| first1 = Albert
| last1 = Gräf
| first2 = Stefan
| last2 = Kersten
| first3 = Yann
| last3 = Orlarey
| title = DSP Programming with Faust, Q and SuperCollider
| journal = Proceedings of the 4th International Linux Audio Conference (LAC2006)
| url = http://lac.zkm.de/2006/papers/lac2006_orlarey_et_al.pdf
| year = 2006
}}
* {{cite journal
| first1 = Robert
| last1 = Trausmuth
| first2 = Christian
| last2 = Dusek
| first3 = Yann
| last3 = Orlarey
| title = Using Faust for FPGA Programming
| journal = Proceedings of the 9th Int. Conference on Digital Audio Effects (DAFx-09)
| url = http://www.dafx.ca/proceedings/papers/p_287.pdf
| year = 2006
}}
* {{Cite book
| first1 = Yann
Line 59 ⟶ 404:
| publisher = Computer Music Association
| url = http://quod.lib.umich.edu/cgi/t/text/text-idx?c=icmc;idno=bbp2372.2005.*
|
| year = 2005
| page = 286
}}
* {{
|
|
| first1 = Yann
| last1 = Orlarey
|
|
| chapter = Syntactical and Semantical Aspects of Faust
|
| 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
|first3=Dominique
|last3=Fober
|first2=Yann
|last2=Orlarey
|title=Automatic Vectorization in Faust
|journal=Journée de l'Informatique Musicale (JIM-2003)
|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
|first2=Dominique
|last2=Fober
|first1=Yann
|last1=Orlarey
|title=An Algebraic Approach to Block Diagram Constructions
|journal=Journée de l'Informatique Musicale (JIM-2002)
|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
|first2=Dominique
|last2=Fober
|first1=Yann
|last1=Orlarey
|title=An Algebra for Block Diagram Languages
|journal=Proceedings of International Computer Music Conference (ICMA-2002)
|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}}
==External links==
{{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]]
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