fluidsynth man page

FluidSynth — a SoundFont synthesizer


fluidsynth [options] [ SoundFonts ]  [ midifiles ]


FluidSynth is a real-time MIDI synthesizer based on the SoundFont(R) 2 specifications. It can be used to render MIDI input or MIDI files to audio.  The MIDI events are read from a MIDI device. The sound is rendered in real-time to the sound output device.

The easiest way to start the synthesizer is to give it a SoundFont on the command line: 'fluidsynth soundfont.sf2'. fluidsynth will load the SoundFont and read MIDI events from the default MIDI device using the default MIDI driver.  Once FluidSynth is running, it reads commands from the stdin. There are commands to send MIDI events manually, to load or unload SoundFonts, and so forth. All the available commands are discussed below.

FluidSynth can also be used to play a list of MIDI files. Simply run FluidSynth with the SoundFont and the list of MIDI files to play. In this case you might not want to open the MIDI device to read external events. Use the -n option to deactivate MIDI input. If you also want to deactivate the use of the shell, start FluidSynth with the -i option: 'fluidsynth -ni soundfont.sf2 midifile1.mid midifile2.mid'.

Run fluidsynth with the --help option to check for changes in the list of options.


fluidsynth accepts the following options:

-a, --audio-driver=[label]

The audio driver to use. "-a help" to list valid options

-c, --audio-bufcount=[count]

Number of audio buffers

-C, --chorus

Turn the chorus on or off [0|1|yes|no, default = on]

-d, --dump

Dump incoming and outgoing MIDI events to stdout

-E, --audio-file-endian

Audio file endian for fast rendering or aufile driver ("-E help" for list)

-f, --load-config

Load command configuration file (shell commands)

-F, --fast-render=[file]

Render MIDI file to raw audio data and store in [file]

-g, --gain

Set the master gain [0 < gain < 10, default = 0.2]

-G, --audio-groups

Defines the number of LADSPA audio nodes

-h, --help

Print out this help summary

-i, --no-shell

Don't read commands from the shell [default = yes]

-j, --connect-jack-outputs

Attempt to connect the jack outputs to the physical ports

-K, --midi-channels=[num]

The number of midi channels [default = 16]

-l, --disable-lash

Don't connect to LASH server

-L, --audio-channels=[num]

The number of stereo audio channels [default = 1]

-m, --midi-driver=[label]

The name of the midi driver to use. "-m help" to list valid options.

-n, --no-midi-in

Don't create a midi driver to read MIDI input events [default = yes]


Define a setting, -o name=value ("-o help" to dump current values)

-O, --audio-file-format

Audio file format for fast rendering or aufile driver ("-O help" for list)

-p, --portname=[label]

Set MIDI port name (alsa_seq, coremidi drivers)

-r, --sample-rate

Set the sample rate

-R, --reverb

Turn the reverb on or off [0|1|yes|no, default = on]

-s, --server

Start FluidSynth as a server process

-T, --audio-file-type

Audio file type for fast rendering or aufile driver ("T help" for list)

-v, --verbose

Print out verbose messages about midi events

-V, --version

Show version of program

-z, --audio-bufsize=[size]

Size of each audio buffer


All settings are non-realtime (have no effect if set after startup), except for those indicated as realtime.

synth.audio-channels INT [min=1, max=128, def=1]

Number of audio channels (DOCME!).

synth.audio-groups INT [min=1, max=128, def=1]

Number of audio groups (DOCME!).

synth.chorus.active BOOL [def=True]

Chorus effect enable toggle.

synth.cpu-cores INT [min=1, max=256, def=1]

Number of CPU cores to use for multi-core support.

synth.device-id INT [min=0, max=126, def=0] REALTIME

Device ID to use for accepting incoming SYSEX messages.

synth.dump BOOL [def=False]

No effect currently.

synth.effects-channels INT [min=2, max=2, def=2]

No effect currently.

synth.gain FLOAT [min=0.000, max=10.000, def=0.200] REALTIME

Master synthesizer gain.

synth.ladspa.active BOOL [def=False]

LADSPA subsystem enable toggle.

synth.midi-channels INT [min=16, max=256, def=16]

Total MIDI channel count (must be multiple of 16).

synth.midi-bank-select STR [def='gs' vals:'gm', 'gs', 'xg', 'mma']

MIDI Bank Select message style.

synth.min-note-length INT [min=0, max=65535, def=10]

Minimum duration for note events (work around for very short percussion notes).

synth.overflow.age FLOAT [min=-10000, max=10000, def=1000]

Weigthing (on overflow) for a voice's duration.

synth.overflow.percussion FLOAT [min=-10000, max=10000, def=4000]

Weighting (on overflow) for a voice being on the drum channel.

synth.overflow.released FLOAT [min=-10000, max=10000, def=-2000]

Weighting (on overflow) for a voice that has been released, i e note off and no sustain pedal.

synth.overflow.sustained FLOAT [min=-10000, max=10000, def=-1000]

Weighting (on overflow) for a voice that has been sustained, i e note off, but sustain pedal held down.

synth.overflow.volume FLOAT [min=-10000, max=10000, def=500]

Weighting (on overflow) for a voice's volume.

synth.parallel-render BOOL [def=True]

Enables low-latency audio rendering response, even if synth is otherwise busy. Should always to be true for usage by fluidsynth executable.

synth.polyphony INT [min=1, max=65535, def=256] REALTIME

Voice polyphony count (number of simultaneous voices allowed).

synth.reverb.active BOOL [def=True]

Reverb effect enable toggle.

synth.sample-rate FLOAT [min=22050.000, max=96000.000, def=44100.000]

Synthesizer sample rate.

synth.threadsafe-api BOOL [def=True]

Serializes access to the synth API. Must always to be true for usage by fluidsynth executable.

synth.verbose BOOL [def=False]

Print received MIDI events to stdout.

audio.driver STR

Audio driver to use. Default and valid options depend on available drivers.

audio.input-channels INT [min=0, max=2, def=0]

Not used currently? (DOCME).

audio.output-channels INT [min=2, max=32, def=2]


audio.period-size INT [min=64, max=8192, def=64]

Period size for audio buffers. Used by many audio drivers.

audio.periods INT [min=2, max=64, def=16]

Count of audio buffers. Used by many audio drivers.

audio.realtime-prio INT [min=0, max=99, def=60]

Realtime priority to assign to audio thread or 0 to disable high priority scheduling. Only used by some audio drivers (currently 'alsa' and 'oss').

audio.sample-format STR [def='16bits' vals:'16bits','float']

Audio output format, to select format for those drivers which support 16 bit or floating point.

audio.alsa.device STR [def='default']

ALSA audio driver output device.

audio.coreaudio.device STR [def='default']

CoreAudio driver output device. Valid options depend on system.

audio.dart.device STR [def='default']

OS/2 Dart audio driver device.

audio.dsound.device STR [def='default']

Device to use for DirectSound driver. Valid options depend on system.

audio.file.endian STR [def='auto' vals:'auto','big','cpu','little']

File renderer or file driver byte order selection. 'auto' selects the default for the selected file type. 'cpu' uses the CPU byte order. Limited to 'cpu' if no libsndfile support.

audio.file.format STR [def='s16' vals:'double','float','s16','s24','s32','s8','u8']

File renderer or file driver audio format. Limited to 's16' if no libsndfile support.

audio.file.name STR [def='fluidsynth.wav']

Output file name for file renderer or file driver.

audio.file.type STR [def='auto' vals:'aiff','au','auto','flac','oga','raw','wav']

Output file type for file renderer or file driver. 'auto' attempts to determine type from file extension in audio.file.name. Limited to 'raw' if no libsndfile support. Actual options will vary depending on libsndfile library.

audio.jack.autoconnect BOOL [def=False]

If enabled, then FluidSynth is automatically connected to Jack system audio output ports.

audio.jack.id STR [def='fluidsynth']

Client ID to use when connecting to Jack.

audio.jack.multi BOOL [def=False]

TRUE to enable multi-channel output.

audio.jack.server STR [def='']

Jack server name. Blank for default.

audio.oss.device STR [def='/dev/dsp']

OSS driver output device.

audio.portaudio.device STR [def='PortAudio Default']

PortAudio driver output device. Available options depends on system.

audio.pulseaudio.adjust-latency BOOL [def=True]

If TRUE initializes the maximum length of the audio buffer to the highest supported value and increases the latency dynamically if PulseAudio suggests so. Else uses a buffer with length of audio.period-size.

audio.pulseaudio.device STR [def='default']

PulseAudio driver output device.

audio.pulseaudio.media-role STR [def='music']

PulseAudio media role information.

audio.pulseaudio.server STR [def='default']

PulseAudio driver server.

midi.driver STR

MIDI driver to use. Default and valid options depend on available drivers.

midi.realtime-prio INT [min=0, max=99, def=50]

Realtime priority to assign to MIDI thread or 0 to disable high priority scheduling. Only used by some MIDI drivers (currently 'alsa_seq', 'alsa_raw' and 'oss').

midi.alsa.device STR [def='default']

ALSA raw MIDI driver device.

midi.alsa_seq.device STR [def='default']

ALSA sequencer MIDI driver device.

midi.alsa_seq.id STR [def='pid']

ALSA sequencer client ID. 'pid' will use process ID as part of the client name.

midi.coremidi.id STR [def='pid']

Client ID to use for CoreMIDI driver. 'pid' will use process ID as port of the client name.

midi.jack.id STR [def='fluidsynth-midi']

Jack MIDI driver client ID.

midi.jack.server STR [def='']

Jack MIDI driver server. Blank to use default.

midi.oss.device STR [def='/dev/midi']

OSS MIDI driver device.

midi.portname STR [def='']

Port name used for CoreAudio and ALSA sequencer drivers.

midi.winmidi.device STR [def='default']

Device for Windows MIDI driver.

player.reset-synth BOOL [def=True]

TRUE to reset synthesizer MIDI state between MIDI songs.

player.timing-source STR [def='sample' vals:'sample','system']

Selects timing source for MIDI sequencer. 'system' uses the system timer. 'sample' uses the sample clock (amount of audio output, events synchronized with audio).

shell.port INT [min=1, max=65535, def=9800]

Shell command server TCP/IP port number to use.

shell.prompt STR [def='']

Shell prompt string.

Shell Commands


Prints out list of help topics (type "help <topic>")


Quit the synthesizer

load filename

Load a SoundFont

unload number

Unload a SoundFont. The number is the index of the SoundFont on the stack.


Lists the current SoundFonts on the stack

inst number

Print out the available instruments for the SoundFont.

noteon channel key velocity

Send a note-on event

noteoff channel key

Send a note-off event

cc channel ctrl value

Send a control change event

prog chan num

Send program-change message

select chan sfont bank prog

Combination of bank-select and program-change


Print out the presets of all channels.

gain value

Set the master gain (0 < gain < 5)

interp num

Choose interpolation method for all channels

interpc chan num

Choose interpolation method for one channel

reverb [0|1|on|off]

Turn the reverb on or off

rev_preset num

Load preset num into the reverb unit

rev_setroomsize num

Change reverb room size

rev_setdamp num

Change reverb damping

rev_setwidth num

Change reverb width

rev_setlevel num

Change reverb level

chorus [0|1|on|off]

Turn the chorus on or off

cho_set_nr n

Use n delay lines (default 3)

cho_set_level num

Set output level of each chorus line to num

cho_set_speed num

Set mod speed of chorus to num (Hz)

cho_set_depth num

Set chorus modulation depth to num (ms)


Reloads the default MIDI routing rules (input channels are mapped 1:1 to the synth)


Deletes all MIDI routing rules.

router_begin [note|cc|prog|pbend|cpress|kpress]

Starts a new routing rule for events of the given type

router_chan min max mul add

Limits the rule for events on min <= chan <= max. If the channel falls into the window, it is multiplied by 'mul', then 'add' is added.

router_par1 min max mul add

Limits parameter 1 (for example note number in a note events). Similar to router_chan.

router_par2 min max mul add

Limits parameter 2 (for example velocity in a note event). Similar to router_chan


Finishes the current rule and adds it to the router.

Router examples
router_begin note
router_chan 0 7 0 15
Will accept only note events from the lower 8 MIDI

channels. Regardless of the channel, the synthesizer plays the note on ch 15 (synthchannel=midichannel*0+15)

router_begin cc
router_chan 0 7 0 15
router_par1 1 1 0 64

Configures the modulation wheel to act as sustain pedal (transforms CC 1 to CC 64 on the lower 8 MIDI channels, routes to ch 15)


Peter Hanappe <hanappe@fluid-synth.org>
Markus Nentwig <nentwig@users.sourceforge.net>
Antoine Schmitt <as@gratin.org>
Josh Green <jgreen@users.sourceforge.net>
Stephane Letz <letz@grame.fr>

Please check the AUTHORS and THANKS files for all credits


SoundFont(R) is a registered trademark of E-mu Systems, Inc.

Referenced By

mscore(1), qsynth(1).

May 5, 2018