A Python FAUST wrapper implemented using the CFFI.
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Marc Joliet marcec@gmx.de

A FAUST wrapper for Python.


FAUSTPy is a Python wrapper for the FAUST DSP language. It is implemented using the CFFI and hence creates the wrapper dynamically at run-time.


FAUSTPy has the following requirements:

  • FAUST, specifically the FAUST2 branch, because FAUSTPy requires the C backend.
  • CFFI, tested with version 0.6.
  • A C compiler; the default CFLAGS assume a GCC compatible one.
  • NumPy, tested with version 1.6.

FAUSTPy works with Python 2.7 and 3.2+.

You can install FAUSTPy via the provided setup.py script by running

sudo python setup.py install


python setup.py install --user

Although you may want to verify that everything works beforehand by running the test suite first:

python setup.py test


Using FAUSTPy is fairly simple, the main class is FAUSTPy.FAUST, which takes care of the dirty work. A typical example:

dsp = FAUSTPy.FAUST("faust_file.dsp", fs)

This will create a wrapper that initialises the FAUST DSP with the sampling rate fs and with FAUSTFLOAT set to the default value of float (the default precision that is set by the FAUST compiler). Note that this

  1. compiles the FAUST DSP to C,
  2. compiles and links the C code, and
  3. initialises the C objects,

all of which happens in the background, thanks to the CFFI. Furthermore, this wrapper class

  1. initialises the UI as a ui attribute of the DSP, and
  2. stores the meta-data declared by the DSP as a metadata attribute.

To better match the NumPy default of double, you can overload the faust_float argument:

dsp = FAUSTPy.FAUST("faust_file.dsp", fs, "double")

To process an array, simply call:

# dsp.dsp is a PythonDSP object wrapped by the FAUST object
audio = numpy.zeros((dsp.dsp.num_in, count))
audio[:,0] = 1
out = dsp.compute(audio)

Here the array audio is initialised to the number of inputs of the DSP and count samples; each channel consists of a Kronecker delta, so out contains the impulse response of the DSP. In general audio is allowed to have more channels (rows) than the DSP, in which case the first dsp.dsp.num_in channels are processed, but not less.

You can also pass in-line FAUST code as the first argument, which will be written to a temporary file and compiled by FAUST as usual. In Python 3:

dsp = FAUSTPy.FAUST(b"process = _:*(0.5);", fs)

Finally, below is a simple IPython example (using Python 2) that shows what a FAUST object might look like. It is based on the DSP dattorro_notch_cut_regalia.dsp included in this repository.

In [1]: import FAUSTPy

In [2]: import numpy as np

In [3]: fs = 48000

In [4]: dattorro = FAUSTPy.FAUST("dattorro_notch_cut_regalia.dsp", fs, "double")

In [5]: dattorro.
dattorro.compute      dattorro.dsp          dattorro.FAUST_PATH
dattorro.compute2     dattorro.FAUST_FLAGS

In [5]: dattorro.dsp.
dattorro.dsp.compute     dattorro.dsp.faustfloat  dattorro.dsp.num_out
dattorro.dsp.compute2    dattorro.dsp.fs          dattorro.dsp.ui
dattorro.dsp.dsp         dattorro.dsp.metadata
dattorro.dsp.dtype       dattorro.dsp.num_in

In [5]: dattorro.dsp.metadata
{'author': 'Marc Joliet',
 'copyright': '(c)Marc Joliet 2013',
 'filter.lib/author': 'Julius O. Smith (jos at ccrma.stanford.edu)',
 'filter.lib/copyright': 'Julius O. Smith III',
 'filter.lib/license': 'STK-4.3',
 'filter.lib/name': 'Faust Filter Library',
 'filter.lib/reference': 'https://ccrma.stanford.edu/~jos/filters/',
 'filter.lib/version': '1.29',
 'license': 'MIT',
 'math.lib/author': 'GRAME',
 'math.lib/copyright': 'GRAME',
 'math.lib/license': 'LGPL with exception',
 'math.lib/name': 'Math Library',
 'math.lib/version': '1.0',
 'music.lib/author': 'GRAME',
 'music.lib/copyright': 'GRAME',
 'music.lib/license': 'LGPL with exception',
 'music.lib/name': 'Music Library',
 'music.lib/version': '1.0',
 'name': 'Dattoro notch filter and resonator (Regalia)',
 'version': '0.1'}

In [6]: dattorro.dsp.fs
Out[6]: 48000

In [7]: dattorro.dsp.num_in
Out[7]: 2

In [8]: dattorro.dsp.num_out
Out[8]: 2

In [9]: dattorro.dsp.ui.
dattorro.dsp.ui.label          dattorro.dsp.ui.metadata       dattorro.dsp.ui.p_Gain
dattorro.dsp.ui.layout         dattorro.dsp.ui.p_Center_Freq  dattorro.dsp.ui.p_Q

In [9]: dattorro.dsp.ui.label
Out[9]: 'dattorro_notch_cut_regalia'

In [10]: dattorro.dsp.ui.layout
Out[10]: 'vertical'

In [11]: dattorro.dsp.ui.p_Center_Freq
Out[11]: <FAUSTPy.python_ui.Param at 0x31617d0>

In [12]: dattorro.dsp.ui.p_Center_Freq.
dattorro.dsp.ui.p_Center_Freq.default   dattorro.dsp.ui.p_Center_Freq.min
dattorro.dsp.ui.p_Center_Freq.label     dattorro.dsp.ui.p_Center_Freq.step
dattorro.dsp.ui.p_Center_Freq.max       dattorro.dsp.ui.p_Center_Freq.type
dattorro.dsp.ui.p_Center_Freq.metadata  dattorro.dsp.ui.p_Center_Freq.zone

In [12]: dattorro.dsp.ui.p_Center_Freq.label
Out[12]: 'Center Freq.'

In [13]: dattorro.dsp.ui.p_Center_Freq.metadata
Out[13]: {'unit': 'Hz'}

In [14]: dattorro.dsp.ui.p_Center_Freq.type
Out[14]: 'HorizontalSlider'

In [15]: audio = np.zeros((dattorro.dsp.num_in,fs), dtype=dattorro.dsp.dtype)

In [16]: audio[:,0] = 1

In [17]: audio
array([[ 1.,  0.,  0., ...,  0.,  0.,  0.],
       [ 1.,  0.,  0., ...,  0.,  0.,  0.]])

In [18]: dattorro.compute(audio)
array([[ 0.74657288, -0.30020767,  0.0227801 , ...,  0.        ,
         0.        ,  0.        ],
       [ 0.74657288, -0.30020767,  0.0227801 , ...,  0.        ,
         0.        ,  0.        ]])

For more details, see the built-in documentation (aka pydoc FAUSTPy) and - if you are so inclined - the source code.

Demo script

The __main__.py of the FAUST package contains a small demo application which plots some magnitude frequency responses of the example FAUST DSP. You can execute it by executing


in the source directory. This will display four plots:

  • the magnitude frequency response of the FAUST DSP at default settings,
  • the magnitude frequency response with varying Q,
  • the magnitude frequency response with varying gain, and
  • the magnitude frequency response with varying center frequency.


  • finish the UIGlue wrapper
  • finish the test suite
    • finish the unit tests
    • add functional tests so that you can test how everything works together (perhaps use "UITester.dsp" and maybe one other DSP from the examples)