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Python bindings for FluidSynth
Copyright 2008, Nathan Whitehead <>
Currently maintained by Bart Spaans <>
Released under the LGPL
This module contains python bindings for FluidSynth. FluidSynth is a
software synthesizer for generating music. It works like a MIDI
synthesizer. You load patches, set parameters, then send NOTEON and
NOTEOFF events to play notes. Instruments are defined in SoundFonts,
generally files with the extension SF2. FluidSynth can either be used
to play audio itself, or you can call a function that returns chunks
of audio data and output the data to the soundcard yourself.
FluidSynth works on all major platforms, so pyFluidSynth should also.
import time
from ctypes import *
from ctypes.util import find_library
# A short circuited or expression to find the FluidSynth library
# (mostly needed for Windows distributions of libfluidsynth supplied with QSynth)
lib = find_library('fluidsynth') or find_library('libfluidsynth') or find_library('libfluidsynth-1')
if lib is None:
raise ImportError, "Couldn't find the FluidSynth library."
# Dynamically link the FluidSynth library
_fl = CDLL(lib)
# Helper function for declaring function prototypes
def cfunc(name, result, *args):
"""Build and apply a ctypes prototype complete with parameter flags"""
atypes = []
aflags = []
for arg in args:
aflags.append((arg[2], arg[0]) + arg[3:])
return CFUNCTYPE(result, *atypes)((name, _fl), tuple(aflags))
# Bump this up when changing the interface for users
api_version = '1.2'
# Function prototypes for C versions of functions
new_fluid_settings = cfunc('new_fluid_settings', c_void_p)
new_fluid_synth = cfunc('new_fluid_synth', c_void_p,
('settings', c_void_p, 1))
new_fluid_audio_driver = cfunc('new_fluid_audio_driver', c_void_p,
('settings', c_void_p, 1),
('synth', c_void_p, 1))
fluid_settings_setstr = cfunc('fluid_settings_setstr', c_int,
('settings', c_void_p, 1),
('name', c_char_p, 1),
('str', c_char_p, 1))
fluid_settings_setnum = cfunc('fluid_settings_setnum', c_int,
('settings', c_void_p, 1),
('name', c_char_p, 1),
('val', c_double, 1))
fluid_settings_setint = cfunc('fluid_settings_setint', c_int,
('settings', c_void_p, 1),
('name', c_char_p, 1),
('val', c_int, 1))
delete_fluid_audio_driver = cfunc('delete_fluid_audio_driver', None,
('driver', c_void_p, 1))
delete_fluid_synth = cfunc('delete_fluid_synth', None,
('synth', c_void_p, 1))
delete_fluid_settings = cfunc('delete_fluid_settings', None,
('settings', c_void_p, 1))
fluid_synth_sfload = cfunc('fluid_synth_sfload', c_int,
('synth', c_void_p, 1),
('filename', c_char_p, 1),
('update_midi_presets', c_int, 1))
fluid_synth_sfunload = cfunc('fluid_synth_sfunload', c_int,
('synth', c_void_p, 1),
('sfid', c_int, 1),
('update_midi_presets', c_int, 1))
fluid_synth_program_select = cfunc('fluid_synth_program_select', c_int,
('synth', c_void_p, 1),
('chan', c_int, 1),
('sfid', c_int, 1),
('bank', c_int, 1),
('preset', c_int, 1))
fluid_synth_noteon = cfunc('fluid_synth_noteon', c_int,
('synth', c_void_p, 1),
('chan', c_int, 1),
('key', c_int, 1),
('vel', c_int, 1))
fluid_synth_noteoff = cfunc('fluid_synth_noteoff', c_int,
('synth', c_void_p, 1),
('chan', c_int, 1),
('key', c_int, 1))
fluid_synth_pitch_bend = cfunc('fluid_synth_pitch_bend', c_int,
('synth', c_void_p, 1),
('chan', c_int, 1),
('val', c_int, 1))
fluid_synth_cc = cfunc('fluid_synth_cc', c_int,
('synth', c_void_p, 1),
('chan', c_int, 1),
('ctrl', c_int, 1),
('val', c_int, 1))
fluid_synth_program_change = cfunc('fluid_synth_program_change', c_int,
('synth', c_void_p, 1),
('chan', c_int, 1),
('prg', c_int, 1))
fluid_synth_bank_select = cfunc('fluid_synth_bank_select', c_int,
('synth', c_void_p, 1),
('chan', c_int, 1),
('bank', c_int, 1))
fluid_synth_sfont_select = cfunc('fluid_synth_sfont_select', c_int,
('synth', c_void_p, 1),
('chan', c_int, 1),
('sfid', c_int, 1))
fluid_synth_program_reset = cfunc('fluid_synth_program_reset', c_int,
('synth', c_void_p, 1))
fluid_synth_system_reset = cfunc('fluid_synth_system_reset', c_int,
('synth', c_void_p, 1))
fluid_synth_write_s16 = cfunc('fluid_synth_write_s16', c_void_p,
('synth', c_void_p, 1),
('len', c_int, 1),
('lbuf', c_void_p, 1),
('loff', c_int, 1),
('lincr', c_int, 1),
('rbuf', c_void_p, 1),
('roff', c_int, 1),
('rincr', c_int, 1))
def fluid_synth_write_s16_stereo(synth, len):
"""Return generated samples in stereo 16-bit format
Return value is a Numpy array of samples.
import numpy
buf = create_string_buffer(len * 4)
fluid_synth_write_s16(synth, len, buf, 0, 2, buf, 1, 2)
return numpy.fromstring(buf[:], dtype=numpy.int16)
def fluid_synth_write_s16_mono(synth, len):
"""Return generated samples in mono 16-bit format
Return value is a Numpy array of samples.
import numpy
buf = create_string_buffer(len * 2)
fluid_synth_write_s16(synth, len, buf, 0, 1, buf, 0, 1)
return numpy.fromstring(buf[:], dtype=numpy.int16)
# Object-oriented interface, simplifies access to functions
class Synth:
"""Synth represents a FluidSynth synthesizer"""
def __init__(self, gain=0.2, samplerate=44100):
"""Create new synthesizer object to control sound generation
Optional keyword arguments:
gain : scale factor for audio output, default is 0.2
lower values are quieter, allow more simultaneous notes
samplerate : output samplerate in Hz, default is 44100 Hz
st = new_fluid_settings()
fluid_settings_setnum(st, 'synth.gain', gain)
fluid_settings_setnum(st, 'synth.sample-rate', samplerate)
# No reason to limit ourselves to 16 channels
fluid_settings_setint(st, 'synth.midi-channels', 256)
self.settings = st
self.synth = new_fluid_synth(st)
self.audio_driver = None
def start(self, driver=None):
"""Start audio output driver in separate background thread
Call this function any time after creating the Synth object.
If you don't call this function, use get_samples() to generate
Optional keyword argument:
driver : which audio driver to use for output
Possible choices:
'alsa', 'oss', 'jack', 'portaudio'
'sndmgr', 'coreaudio', 'Direct Sound'
Not all drivers will be available for every platform, it
depends on which drivers were compiled into FluidSynth for
your platform.
if driver is not None:
assert (driver in ['alsa', 'oss', 'jack', 'portaudio', 'sndmgr', 'coreaudio', 'Direct Sound'])
fluid_settings_setstr(self.settings, 'audio.driver', driver)
self.audio_driver = new_fluid_audio_driver(self.settings, self.synth)
def delete(self):
if self.audio_driver is not None:
def sfload(self, filename, update_midi_preset=0):
"""Load SoundFont and return its ID"""
return fluid_synth_sfload(self.synth, filename, update_midi_preset)
def sfunload(self, sfid, update_midi_preset=0):
"""Unload a SoundFont and free memory it used"""
return fluid_synth_sfunload(self.synth, sfid, update_midi_preset)
def program_select(self, chan, sfid, bank, preset):
"""Select a program"""
return fluid_synth_program_select(self.synth, chan, sfid, bank, preset)
def noteon(self, chan, key, vel):
"""Play a note"""
if key < 0 or key > 128:
return False
if chan < 0:
return False
if vel < 0 or vel > 128:
return False
return fluid_synth_noteon(self.synth, chan, key, vel)
def noteoff(self, chan, key):
"""Stop a note"""
if key < 0 or key > 128:
return False
if chan < 0:
return False
return fluid_synth_noteoff(self.synth, chan, key)
def pitch_bend(self, chan, val):
"""Adjust pitch of a playing channel by small amounts
A pitch bend value of 0 is no pitch change from default.
A value of -2048 is 1 semitone down.
A value of 2048 is 1 semitone up.
Maximum values are -8192 to +8192 (transposing by 4 semitones).
return fluid_synth_pitch_bend(self.synth, chan, val + 8192)
def cc(self, chan, ctrl, val):
"""Send control change value
The controls that are recognized are dependent on the
SoundFont. Values are always 0 to 127. Typical controls
1 : vibrato
7 : volume
10 : pan (left to right)
11 : expression (soft to loud)
64 : sustain
91 : reverb
93 : chorus
return fluid_synth_cc(self.synth, chan, ctrl, val)
def program_change(self, chan, prg):
"""Change the program"""
return fluid_synth_program_change(self.synth, chan, prg)
def bank_select(self, chan, bank):
"""Choose a bank"""
return fluid_synth_bank_select(self.synth, chan, bank)
def sfont_select(self, chan, sfid):
"""Choose a SoundFont"""
return fluid_synth_sfont_select(self.synth, chan, sfid)
def program_reset(self):
"""Reset the programs on all channels"""
return fluid_synth_program_reset(self.synth)
def system_reset(self):
"""Stop all notes and reset all programs"""
return fluid_synth_system_reset(self.synth)
def get_samples(self, len=1024):
"""Generate audio samples
The return value will be a NumPy array containing the given
length of audio samples. If the synth is set to stereo output
(the default) the array will be size 2 * len.
return fluid_synth_write_s16_stereo(self.synth, len)
def get_mono_samples(self, len=1024):
return fluid_synth_write_s16_mono(self.synth, len)
def raw_audio_string(data):
"""Return a string of bytes to send to soundcard
Input is a numpy array of samples. Default output format
is 16-bit signed (other formats not currently supported).
import numpy
return (data.astype(numpy.int16)).tostring()
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