pure-lang / pure-faust /

Filename Size Date modified Message
34.3 KB
7.5 KB
2.7 KB
13.3 KB
43.5 KB
22.7 KB
2.0 KB
2.7 KB

.. default-domain:: pure
.. module:: faust

Version @version@, |today|

Albert Graef <>

This module lets you load and run Faust-generated signal processing modules in
Pure_. Faust_ (an acronym for Functional AUdio STreams) is a functional
programming language for real-time sound processing and synthesis developed at
Grame_ and distributed as GPL'ed software.

.. note::

   As of Pure 0.45, there's also built-in support for Faust interoperability
   in the Pure core, including the ability to inline Faust code in Pure
   programs; see :ref:`Interfacing to Faust` in the Pure manual.  The built-in
   Faust interface requires Faust2_ which is still under development and
   available as a separate package in the Faust git repository.  Both
   interfaces provide pretty much the same basic capabilities and should work
   equally well for most applications. In fact, as of version 0.5 pure-faust
   comes with a compatibility module which provides the pure-faust API on top
   of the built-in Faust interface, see the description of the :mod:`faust2`
   module below for details.

.. _Faust:
.. _Faust2:
.. _Grame:
.. _Pure:


Unless explicitly stated otherwise, this software is Copyright (c) 2009-2012
by Albert Graef. Please also see the source for the copyright and license
notes pertaining to individual source files.

pure-faust is free software: you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the Free
Software Foundation, either version 3 of the License, or (at your option) any
later version.

pure-faust is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more

You should have received a copy of the GNU Lesser General Public License along
with this program.  If not, see <>.


Get the latest source from

Binary packages can be found at To install
from source, run the usual ``make && sudo make install``. This requires Pure,
of course (the present version will work with Pure 0.52 and later). The
Makefile tries to guess the installation prefix under which Pure is
installed. If it guesses wrong, you can tell it the right prefix with ``make
prefix=/some/path``. Or you can specify the exact path of the ``lib/pure``
directory with ``make libdir=/some/path``; by default the Makefile assumes
``$(prefix)/lib/pure``. The Makefile also tries to guess the host system type
and set up some platform-specific things accordingly. If this doesn't work for
your system then you'll have to edit the Makefile accordingly.

The Faust compiler is not required to compile this module, but of course
you'll need it to build the examples in the ``examples`` subdirectory and to
compile your own Faust sources. You'll need Faust 0.9.46 or later.

To compile Faust programs for use with this module, you'll also need the
``pure.cpp`` architecture file. This should be included in recent Faust
releases. If your Faust version doesn't have it yet, you can find a suitable
version of this file in the ``examples`` folder. Simply copy the file to your
Faust library directory (usually ``/usr/local/lib/faust`` or similar) or the
directory holding the Faust sources to be compiled, and you should be set.


Once Faust and this module have been installed as described above, you should
be able to compile a Faust dsp to a shared module loadable by pure-faust as

  $ faust -a pure.cpp -o mydsp.cpp mydsp.dsp
  $ g++ -shared -o mydsp.cpp

Note that, by default, Faust generates code which does all internal
computations with single precision. You can add the ``-double`` flag to the
Faust command in order to use double precision instead. (In either case, all
data will be represented as doubles on the Pure side.)

Also note that the above compile command is for a Linux or BSD system using
``gcc``. Add ``-fPIC`` for 64 bit compilation. For Windows compilation, the
output filename should be ``mydsp.dll`` instead of ````; on Mac OSX,
it should be ``mydsp.dylib``. There's a Makefile in the ``examples`` folder
which automates this process.

Once the module has been compiled, you can fire up the Pure interpreter and
load the dsp as follows::

  > using faust;
  > let dsp = faust_init "mydsp" 48000;
  > dsp;
  #<pointer 0xf09220>

The ``faust_init`` function loads the ``""`` module (the ``.so``
suffix is supplied automatically) and returns a pointer to the Faust dsp
object which can then be used in subsequent operations.

.. note:: ``faust_init`` only loads the dsp module if it hasn't been loaded
   before. However, as of pure-faust 0.8, ``faust_init`` also checks the
   modification time of the module and reloads it if the module was recompiled
   since it was last loaded. (This is for compatibility with Pure's built-in
   Faust interface which behaves in the same way.) If this happens, *all*
   existing dsp instances created with the old version of the module become
   invalid immediately (i.e., all subsequent operations on them will fail,
   except ``faust_exit``) and must be recreated.

The second parameter of ``faust_init``, 48000 in this example, denotes the
sample rate in Hz. This can be an arbitrary integer value which is available
to the hosted dsp (it's up to the dsp whether it actually uses this value in
some way). The sample rate can also be changed on the fly with the
``faust_reinit`` function::

  > faust_reinit dsp 44100;

It is also possible to create copies of an existing dsp with the
``faust_clone`` function, which is quite handy if multiple copies of the same
dsp are needed (a case which commonly arises when implementing polyphonic

  > let dsp2 = faust_clone dsp;

When you're done with a dsp, you can invoke the ``faust_exit`` function to
unload it (this also happens automatically when a dsp object is

  > faust_exit dsp2;

Note that after invoking this operation the dsp pointer becomes invalid and
must not be used any more.

In the following, we use the following little Faust program as a running

  declare descr "amplifier";
  declare author "Albert Graef";
  declare version "1.0";

  gain = nentry("gain", 1.0, 0, 10, 0.01);
  process = *(gain);

The ``faust_info`` function can be used to determine the number of
input/output channels as well as the "UI" (a data structure describing the
available control variables) of the loaded dsp::

  > let n,m,ui = faust_info dsp;

Global metadata of the dsp is available as a list of ``key=>val`` string pairs
with the ``faust_meta`` function. For instance::

  > faust_meta dsp;
  ["descr"=>"amplifier","author"=>"Albert Graef","version"=>"1.0"]

To actually run the dsp, you'll need two buffers capable of holding the
required number of audio samples for input and output. For convenience, the
``faust_compute`` routine lets you specify these as Pure double matrices.
``faust_compute`` is invoked as follows::

  > faust_compute dsp in out;

Here, ``in`` and ``out`` must be double matrices which have at least ``n`` or
``m`` rows, respectively (corresponding to the number of input and output
channels of the Faust dsp). The row size of these matrices determines the
number of samples which will be processed (if one of the matrices has a larger
row size than the other, the extra elements are ignored). The ``out`` matrix
will be modified in-place and also returned as the result of the call.

Some DSPs (e.g., synthesizers) only take control input without processing any
audio input; others (e.g., pitch detectors) might produce just control output
without any audio output. In such cases you can just specify an empty ``in``
or ``out`` matrix, respectively. For instance::

  > faust_compute dsp {} out;

Most DSPs take additional control input. The control variables are listed in
the "UI" component of the ``faust_info`` return value. For instance, suppose
that there's a ``gain`` parameter listed there, it might look as follows::

  > controls ui!0;
  hslider #<pointer 0x12780a4> [] ("gain",1.0,0.0,10.0,0.1)

The constructor itself denotes the type of control, which matches the name of
the Faust builtin used to create the control (see the Faust documentation for
more details on this). The *third* parameter is a tuple which indicates the
arguments the control was created with in the Faust program. The *first*
parameter is a C ``double*`` which points to the current value of the control
variable. You can inspect and change this value with the ``get_double`` and
``put_double`` routines available in the Pure prelude. (Note that, for
compatibility with the internal Faust interface which supports both single and
double precision controls, you can also use the ``get_control`` and
``put_control`` functions instead.) Changes of control variables only take
effect between different invocations of ``faust_compute``. Example::

  > let gain = control_ref (controls ui!0);
  > get_double gain;
  > put_double gain 2.0;
  > faust_compute dsp in out;

Output controls such as ``hbargraph`` and ``vbargraph`` are handled in a
similar fashion, only that the Faust dsp updates these values for each call to
``faust_compute`` and Pure scripts can then read the values with
``get_double`` or ``get_control``.

The *second* parameter of a control description is a list holding the Faust
metadata of the control. This list will be empty if the control does not have
any metadata.  Otherwise you will find some of ``key=>val`` string pairs in
this list. It is completely up to the application how to interpret the
metadata, which may consist, e.g., of GUI layout hints or various kinds of
controller definitions. For instance, a MIDI controller assignment might look
as follows in the Faust source::

  gain = nentry("gain[midi:ctrl 7]", 1.0, 0, 10, 0.01);

In Pure this information will then be available as::

  > control_meta (controls ui!0);
  ["midi"=>"ctrl 7"]

Let's finally have a closer look at the contents of the UI data structure. You
will find that it is actually a tree, similar to the directory tree of a
hierarchical file system, which reflects the layout of the controls in the
Faust program. For instance::

  > ui;
  vgroup [] ("mydsp",[nentry #<pointer 0x12780a4> [] ("gain",1.0,0.0,10.0,0.01)])

The leaves of the tree are the actual controls, while its interior nodes are
so-called "control groups", starting from a root node which represents the
entire dsp. There are different kinds of control groups such as ``vgroup`` and
``hgroup``; please check the Faust documentation for details. Control groups
have a name and metadata just like individual controls, but there is no
``control_ref`` component and the data stored at the node is the list of
controls and subgroups contained in the control group. The ``controls``
function returns a flat representation of the controls in the UI tree as a
list, omitting the group nodes of the tree::

  > controls ui;
  [hslider #<pointer 0x12780a4> [] ("gain",1.0,0.0,10.0,0.1)]

We've already employed this function above to extract the ``gain`` control of
our example dsp. There's a variation of this function which yields the full
"pathnames" of controls in the UI tree::

  > pcontrols ui;
  [hslider #<pointer 0x12780a4> [] ("mydsp/gain",1.0,0.0,10.0,0.1)]

This is sometimes necessary to distinguish controls with identical names in
different control groups. There are two additional convenience functions which
work with this flat representation of the UI data structure::

  > let ctrls = ans;
  > control_map ctrls;
  {"mydsp/gain"=>#<pointer 0x12780a4>}
  > control_metamap ctrls;

The results are Pure records which provide convenient access to the pointers
and metadata of the controls by their name.

Please note that, as of Pure 0.45, the UI access functions described above are
actually provided by the :mod:`faustui` standard library module which gets
included by the :mod:`faust` module.

Further examples can be found in the examples subdirectory.

Faust2 Compatibility

.. module:: faust2

As of version 0.5, pure-faust includes a Faust2 compatibility module which
lets you use the pure-faust API on top of Pure's new Faust bitcode interface,
using the same operations as described under Usage_ above. This module is
invoked with the following import clause::

  using faust2;

To instantiate a Faust dsp using the :mod:`faust2` interface, you'll have to
compile the Faust program to LLVM bitcode format. The examples directory
includes a ``pure.c`` Faust architecture file to help with this. Please see
the :ref:`Interfacing to Faust` section in the Pure manual for details.

Note that only one of the :mod:`faust` and :mod:`faust2` modules may be
imported into a program; trying to use both modules in the same program will
*not* work. Also note that the :mod:`faust2` module requires Faust2_ and a
fairly recent Pure version to work, whereas the :mod:`faust` module works with
both Faust2 and the mainline Faust version and doesn't rely on the Faust
bitcode loader (only the ``pure.cpp`` architecture is needed).


Many thanks to Yann Orlarey at Grame, the principal author of Faust!

.. Enjoy. :)