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# pure-faust: Run Faust programs in Pure scripts

Version 0.4, February 09, 2011

Albert Graef <Dr.Graef@t-online.de>

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

This module is now largely obsolete as there’s much better direct support for Faust interoperability in the Pure core (as of Pure 0.45), including the ability to inline Faust code in Pure programs. This requires faust2 (the latest Faust incarnation from Faust’s git repository), however, so this package is still provided for those who are stuck with older faust versions.

## Copying

Unless explicitly stated otherwise, this software is Copyright (c) 2009 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 details.

You should have received a copy of the GNU Lesser General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.

## Installation

Get the latest source from http://pure-lang.googlecode.com/files/pure-faust-0.4.tar.gz.

Binary packages can be found at http://pure-lang.googlecode.com/. To install from source, run the usual `make && sudo make install`. This requires Pure, of course. 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 0.9.9.6 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. (Note that `pure.cpp` is distributed under a simple all-permissive license, so you can use it for pretty much any purpose, including commercial applications.)

## Usage

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 follows:

    $ faust -a pure.cpp -o mydsp.cpp mydsp.dsp
    $ g++ -shared -o mydsp.so 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 `mydsp.so`; 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 `"mydsp.so"` module (the `.so` suffix is supplied automatically) and returns a pointer to the Faust DSP object which can then be used in subsequent operations. 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 synthesizers):

    > 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 garbage-collected):

    > faust_exit dsp2;

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

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;

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 of the same row size (which corresponds to the number of samples which will be processed) which have at least `n` or `m` rows, respectively (corresponding to the number of input and output channels of the Faust DSP). 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 second 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 changes of control variables only take effect between different invokations of `faust_compute`.) Example:

    > let gain = control_ref (controls ui!0);
    > get_double gain;
    1.0
    > 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`.

Ok, I hope that this is enough to get you started. Further examples can be found in the examples subdirectory. Please send bug reports, patches, comments and suggestions to: Dr.Graef@t-online.de.

## Acknowledgements

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

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