FAUST (programming language): Difference between revisions

Revision as of 16:31, 11 April 2020

Revision as of 17:45, 11 May 2020

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* 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):

<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. 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==