audio-channels int 1 1 128 By default, the synthesizer outputs a single stereo signal. Using this option, the synthesizer can output multi-channel audio. Sets the number of stereo channel pairs. So 1 is actually 2 channels (a stereo pair). audio-groups int 1 1 128 The output audio channel associated with a MIDI channel is wrapped around using the number of synth.audio-groups as modulo divider. This is typically the number of output channels on the sound card, as long as the LADSPA Fx unit is not used. In case of LADSPA unit, think of it as subgroups on a mixer. chorus.active bool 1 (TRUE) When set to 1 (TRUE) the chorus effects module is activated. Otherwise, no chorus will be added to the output signal. Note that the amount of signal sent to the chorus module depends on the "chorus send" generator defined in the SoundFont. chorus.depth num 4.25 (since version 2.4.0),
8.0 (2.3.x and older) 0.0 256.0 Specifies the modulation depth of the chorus. chorus.level num 0.6 (since version 2.4.0),
2.0 (2.3.x and older) 0.0 10.0 Specifies the output amplitude of the chorus signal. chorus.nr int 3 0 99 Sets the voice count of the chorus. chorus.speed num 0.2 (since version 2.4.0),
0.3 (2.3.x and older) 0.1 5.0 Sets the modulation speed in Hz. cpu-cores int 1 1 256 Sets the number of synthesis CPU cores. If set to a value greater than 1, additional synthesis threads will be created to do the actual rendering work that is then returned synchronously by the render function. This has the affect of utilizing more of the total CPU for voices or decreasing render times when synthesizing audio. So for example, if you set cpu-cores to 4, fluidsynth will attempt to split the synthesis work it needs to do between the client's calling thread and three additional (internal) worker threads. As soon as all threads have done their work, their results are collected and the resulting buffer is returned to the caller. default-soundfont str C:\soundfonts\default.sf2 (Windows),
${CMAKE_INSTALL_PREFIX}/share/soundfonts/default.sf2 (all others) The default soundfont file to use by the fluidsynth executable. The default value can be overridden during compilation time by setting the DEFAULT_SOUNDFONT cmake variable. device-id int 0 0 127 Device identifier used for SYSEX commands, such as MIDI Tuning Standard commands. Fluidsynth will only process those SYSEX commands destined for this ID (except when this setting is set to 127, which causes fluidsynth to process all SYSEX commands, regardless of the device ID). Broadcast commands (with ID=127) will always be processed. It has been observed that setting this ID to 16 provides best compatibility when playing MIDI files which contain SYSEX commands that you want to have honored. dynamic-sample-loading bool 0 (FALSE) When set to 1 (TRUE), samples are loaded to and unloaded from memory whenever presets are being selected or unselected for a MIDI channel (PROGRAM_CHANGE and PROGRAM_SELECT events are typically responsible for this). This involves memory allocation, which is not realtime safe! So only enable this in non-realtime scenarios! E.g. when rendering to a WAVE file using the fast-file-renderer. effects-channels int 2 2 2 Specifies the number of effects per effects group. Currently this value can not be changed so there are always two effects per group available (reverb and chorus). effects-groups int 1 1 128 Specifies the number of effects groups. By default, the sound of all voices is rendered by one reverb and one chorus effect respectively (even for multi-channel rendering). This setting gives the user control which effects of a voice to render to which independent audio channels. E.g. setting synth.effects-groups == synth.midi-channels allows to render the effects of each MIDI channel to separate audio buffers. If synth.effects-groups is smaller than the number of MIDI channels, it will wrap around. Note that any value >1 will significantly increase CPU usage. gain num 0.2 0.0 10.0 The gain is applied to the final or master output of the synthesizer, but before it will be processed by the limiter (if enabled). It is set to a low value by default to avoid the saturation of the output when many notes are played. ladspa.active bool 0 (FALSE) When set to 1 (TRUE) the LADSPA subsystem will be enabled. This subsystem allows to load and interconnect LADSPA plug-ins. The output of the synthesizer is processed by the LADSPA subsystem. Note that the synthesizer has to be compiled with LADSPA support. More information about the LADSPA subsystem can be found in doc/ladspa.md or on the FluidSynth website. limiter.active bool 0 (FALSE) When set to 1 (TRUE) a look-ahead limiter is added at the end of fluidsynth's audio processing chain. This limiter helps to prevent clipping and distortion by limiting the gain of the output signal. Note that fluidsynth has to be compiled with limiter support, otherwise any of the limiter related settings will return FLUID_FAILED when attempting to set or get them. limiter.attack num 5 1 250 When the limiter "sees" an incoming gain-peak, the attack specifies the look-ahead time in milliseconds, i.e. how much time before that peak the output gain will start to be reduced. Higher values allow the limiter to react more smoothly, but also increase latency because the generated audio must be delayed accordingly. limiter.hold num 15 0 250 Specifies the time in milliseconds how long the previously reduced ("damped") output gain is maintained (after the gain-peak has passed), before the limiter begins to return to the normal gain level. limiter.release num 40 0 250 Specifies the time in milliseconds how quickly the output gain returns towards the normal level after the gain-peak has passed and the hold phase has completed. limiter.output-limit num 0.99999 0.063 (i.e. 240dB of attenuation) 1 (i.e. 0dB of attenuation) Specifies the target output limit of the limiter in linear range and therefore the final output level of fluidsynth's synthesized audio. The audio input for the limiter is amplified by the synth.gain setting. limiter.smoothing-stages int 1 1 3 Controls how strongly the limiter smooths sudden gain changes. A value of 1 uses a single smoothing stage and gives the fastest response. Values of 2 or 3 apply additional smoothing to the gain envelope, which can reduce distortion and pumping artifacts at the cost of a slightly slower reaction and longer release. limiter.link-channels num 0.5 0 1 Specifies how closely the limiter gains of all output channels (i.e. the left and right channels of a stereo output) are linked together. A value of 1.0 applies the same gain to all channels, based on the loudest channel. A value of 0.0 lets each channel be limited independently. Intermediate values interpolate between these behaviours. lock-memory bool 1 (TRUE) Page-lock memory that contains audio sample data, if true. midi-channels int 16 16 256 This setting defines the number of MIDI channels of the synthesizer. The MIDI standard defines 16 channels, so MIDI hardware is limited to this number. Internally FluidSynth can use more channels which can be mapped to different MIDI sources. midi-bank-select str gs gs, gm, xg, mma This setting defines how the synthesizer interprets Bank Select messages.

• gs: (default) CC0 becomes the bank number, CC32 is ignored.
• gm: ignores CC0 and CC32 messages.
• mma: bank is calculated as CC0*128+CC32.
• xg: If CC0 is equal to 120, 126, or 127 then channel is set to drum mode and the bank number is set to 128. CC32 is ignored in this case. If CC0 has a different value, the channel is set to melodic and CC32 becomes the bank number. Note that before fluidsynth 2.3.5 the logic for CC0 was broken.

min-note-length int 10 0 65535 Sets the minimum note duration in milliseconds. This ensures that really short duration note events, such as percussion notes, have a better chance of sounding as intended. Set to 0 to disable this feature. note-cut int 0 0 2 This setting specifies the behavior for releasing voices, if the same note is hit twice on the same channel. Early synthesizers like the Roland SC-55 and Microsoft Wavetable GS MIDI synthesizer (MSGS) are terminating notes abruptly that have already received a noteOff after receiving a noteOn for the same key. This behavior was presumably implemented to save polyphony in these systems. This setting was introduced in fluidsynth 2.4.3 and can be enabled to mimic this behavior, to esp. play back old tunes like Doom E1M1 more accurately. Please note that using a SoundFont which makes proper use of exclusive classes for esp. percussion instruments will yield a similar or better result. Also, this approach is generally preferable because it's portable among SF2 compliant synths and can be applied more fine-grained among instruments. This setting supports the following values:

• 0: A regular noteOff is applied to the previous note, which is the default SF2 compliant behavior.
• 1: Note-cut is only applied on drum MIDI channels (i.e. CHANNEL_TYPE_DRUM). Fluidsynth 2.4.0, 2.4.1, and 2.4.2 unconditionally used this mode.
• 2: Note-cut is applied to both, drum and melodic MIDI channels (i.e. CHANNEL_TYPE_DRUM and CHANNEL_TYPE_MELODIC).

overflow.age num 1000.0 -10000.0 10000.0 This score is divided by the number of seconds this voice has been active and is added to the overflow priority. It is usually a positive value and gives voices which have just been started a higher priority, making them less likely to be killed in an overflow situation. overflow.important num 5000.0 -50000.0 50000.0 This score is added to voices on channels marked with the synth.overflow.important-channels setting. overflow.important-channels str (empty string) This setting is a comma-separated list of MIDI channel numbers that should be treated as "important" by the overflow calculation, adding the score set by synth.overflow.important to each voice on those channels. It can be used to make voices on particular MIDI channels less likely (synth.overflow.important > 0) or more likely (synth.overflow.important < 0) to be killed in an overflow situation. Channel numbers are 1-based, so the first MIDI channel is number 1. overflow.percussion num 4000.0 -10000.0 10000.0 Sets the overflow priority score added to voices on a percussion channel. This is usually a positive score, to give percussion voices a higher priority and less chance of being killed in an overflow situation. overflow.released num -2000.0 -10000.0 10000.0 Sets the overflow priority score added to voices that have already received a note-off event. This is usually a negative score, to give released voices a lower priority so that they are killed first in an overflow situation. overflow.sustained num -1000.0 -10000.0 10000.0 Sets the overflow priority score added to voices that are currently sustained. With the default value, sustained voices are considered less important and are more likely to be killed in an overflow situation. overflow.volume num 500.0 -10000.0 10000.0 Sets the overflow priority score added to voices based on their current volume. The voice volume is normalized to a value between 0 and 1 and multiplied with this setting. So voices with maximum volume get added the full score, voices with only half that volume get added half of this score. polyphony int 256 1 65535 The polyphony defines how many voices can be played in parallel. A note event produces one or more voices. Its good to set this to a value which the system can handle and will thus limit FluidSynth's CPU usage. When FluidSynth runs out of voices it will begin terminating lower priority voices for new note events. portamento-time str auto auto, linear, xg-gs This setting was introduced in 2.5.0 to specify how to handle portamento time CC MSB and LSB.

• 'linear' - portamento time is 14 bits wide and calculated as CC5 * 128 + CC37 in milliseconds (this was fluidsynth's behavior before this setting was introduced).
• 'xg-gs' - portamento time is 7 bits wide, using only CC5, which is mapped onto a concave curve ranging from 0s to 480s. The exact mapping was derived through listening tests and may be subject to change between different versions of fluidsynth. This setting should be used for older MIDI files, like Descent Game08.
• 'auto' - the synth starts in 'xg-gs' mode. If it detects a CC37 on any MIDI channel, it switches to 'linear' mode.

reverb.active bool 1 (TRUE) When set to 1 (TRUE) the reverb effects module is activated. Otherwise, no reverb will be added to the output signal. Note that the amount of signal sent to the reverb module depends on the "reverb send" generator defined in the SoundFont. reverb.damp num 0.3 (since version 2.4.0),
0.0 (2.3.x and older) 0.0 1.0 Sets the amount of reverb damping. reverb.level num 0.7 (since version 2.4.0),
0.9 (2.3.x and older) 0.0 1.0 Sets the reverb output amplitude. reverb.room-size num 0.5 (since version 2.4.0),
0.2 (2.3.x and older) 0.0 1.0 Sets the room size (i.e. amount of wet) reverb. reverb.width num 0.8 (since version 2.4.0),
0.5 (2.3.x and older) 0.0 100.0 Sets the stereo spread of the reverb signal. A value of 0 indicates no stereo-separation causing the reverb to sound like a monophonic signal. A value of 1 indicates maximum separation between the uncorrelated left and right channels (note that reverb is still a monophonic effect). This subrange [0;1] is recommended for general usage. Values bigger than 1 increase (or exaggerate) the perception of the uncorrelated left and right signals. Otherwise, this setting should be considered as dimensionless quantity, with its maximum value existing for historical reasons. Please note that under some circumstances, values bigger than 1 may induce a feedback into the signal which can be perceived as unpleasant. sample-rate num 44100.0 8000.0 96000.0 The sample rate of the audio generated by the synthesizer. For optimal performance, make sure this value equals the native output rate of the audio driver (in case you are using any of FluidSynth's audio drivers). Some drivers, such as Oboe, will interpolate sample rates, whereas others, such as JACK, will override this setting if a mismatch with the native output rate is detected.

Important: This setting should not be changed during runtime of the synthesizer.

The sample rate is applied when the synthesizer is created and controls the rate at which samples are synthesized. Changing this value after creating the synthesizer does not affect the synthesizer. Audio drivers created later may use the updated setting value and cause the audio to play out of tune. If you need to change the sample rate, recreate both the synthesizer and the audio driver using settings with the new sample rate. threadsafe-api bool 1 (TRUE) Controls whether the synth's public API is protected by a mutex or not. Default is on, turn it off for slightly better performance if you know you're only accessing the synth from one thread only, this could be the case in many embedded use cases for example. Note that libfluidsynth can use many threads by itself (shell is one, midi driver is one, midi player is one etc) so you should usually leave it on. verbose bool 0 (FALSE) When set to 1 (TRUE) the synthesizer will print out information about the received MIDI events to the stdout. This can be helpful for debugging. This setting cannot be changed after the synthesizer has started. autoconnect bool 0 (FALSE) If 1 (TRUE), automatically connects FluidSynth to available MIDI input ports. alsa_seq, coremidi and jack are currently the only drivers making use of this. driver str alsa_seq (Linux),
winmidi (Windows),
jack (Mac OS X) alsa_raw, alsa_seq, coremidi, jack, midishare, oss, winmidi The MIDI system to be used. realtime-prio int 50 0 99 Sets the realtime scheduling priority of the MIDI thread (0 disables high priority scheduling). Linux is the only platform which currently makes use of different priority levels. Drivers which use this option: alsa_raw, alsa_seq, oss portname str (empty string) Used by coremidi and alsa_seq drivers for the portnames registered with the MIDI subsystem. alsa.device str default ALSA MIDI hardware device to use for RAW ALSA MIDI driver (not to be confused with the MIDI port). Since fluidsynth 2.3.0 this setting will be populated with available devices when fluidsynth starts up. alsa_seq.device str default ALSA sequencer hardware device to use for ALSA sequencer driver (not to be confused with the MIDI port). alsa_seq.id str pid ID to use when registering ports with the ALSA sequencer driver. If set to "pid" then the ID will be "FLUID Synth (PID)", where PID is the FluidSynth process ID of the audio thread otherwise the provided string will be used in place of PID. coremidi.id str pid Client ID to use for CoreMIDI driver. 'pid' will use process ID as port of the client name. jack.server str (empty string) Jack server to connect to for Jack MIDI driver. If an empty string then the default server will be used. jack.id str fluidsynth-midi Client ID to use with the Jack MIDI driver. If jack is also used as audio driver and "midi.jack.server" and "audio.jack.server" are equal, this setting will be overridden by "audio.jack.id", because a client cannot have multiple names. oss.device str /dev/midi The hardware device to use for OSS MIDI driver (not to be confused with the MIDI port). winmidi.device str default The hardware device to use for Windows MIDI driver (not to be confused with the MIDI port). Multiple devices can be specified by a list of devices index separated by a semicolon (e.g "2;0", which is equivalent to one device with 32 MIDI channels). Starting with 2.3.6 all device names are expected to be UTF8 encoded. reset-synth bool 1 (TRUE) If true, reset the synth after the end of a MIDI song, so that the state of a previous song can't affect the next song. Turn it off for seamless looping of a song. timing-source str sample sample, system Determines the timing source of the player sequencer. 'sample' uses the sample clock (how much audio has been output) to sequence events, in which case audio is synchronized with MIDI events. 'system' uses the system clock, audio and MIDI are not synchronized exactly. prompt str (empty string) In dump mode we set the prompt to "" (empty string). The ui cannot easily handle lines, which don't end with cr. Changing the prompt cannot be done through a command, because the current shell does not handle empty arguments. port int 0 0 65535 The shell can be used in a client/server mode. This setting controls what TCP/IP port the server uses. Since fluidsynth 2.5.4, a value of 0 enables auto mode and selects the first free port, probing from 9800 upwards. Older versions used 9800 as default port. Note that when set to 0, fluidsynth will update the setting during server creation (new_fluid_server2()) with the actual port number used.