Synthesis Parameters

Functions to control and query synthesis parameters like gain and polyphony count. More...

Enumerations
enum	fluid_interp {   FLUID_INTERP_NONE = 0 ,   FLUID_INTERP_LINEAR = 1 ,   FLUID_INTERP_4THORDER = 4 ,   FLUID_INTERP_7THORDER = 7 ,   FLUID_INTERP_DEFAULT = FLUID_INTERP_4THORDER ,   FLUID_INTERP_HIGHEST = FLUID_INTERP_7THORDER }
	Synthesis interpolation method. More...
enum	fluid_synth_add_mod {   FLUID_SYNTH_OVERWRITE ,   FLUID_SYNTH_ADD }
	Enum used with fluid_synth_add_default_mod() to specify how to handle duplicate modulators. More...

Functions
int	fluid_synth_add_default_mod (fluid_synth_t *synth, const fluid_mod_t *mod, int mode)
	Adds the specified modulator mod as default modulator to the synth. More...
int	fluid_synth_count_audio_channels (fluid_synth_t *synth)
	Get the total count of audio channels. More...
int	fluid_synth_count_audio_groups (fluid_synth_t *synth)
	Get the total number of allocated audio channels. More...
int	fluid_synth_count_effects_channels (fluid_synth_t *synth)
	Get the total number of allocated effects channels. More...
int	fluid_synth_count_effects_groups (fluid_synth_t *synth)
	Get the total number of allocated effects units. More...
int	fluid_synth_count_midi_channels (fluid_synth_t *synth)
	Get the total count of MIDI channels. More...
int	fluid_synth_get_active_voice_count (fluid_synth_t *synth)
	Get current number of active voices. More...
float	fluid_synth_get_gain (fluid_synth_t *synth)
	Get synth output gain value. More...
int	fluid_synth_get_internal_bufsize (fluid_synth_t *synth)
	Get the internal synthesis buffer size value. More...
int	fluid_synth_get_polyphony (fluid_synth_t *synth)
	Get current synthesizer polyphony (max number of voices). More...
int	fluid_synth_remove_default_mod (fluid_synth_t *synth, const fluid_mod_t *mod)
	Removes the specified modulator mod from the synth's default modulator list. More...
void	fluid_synth_set_gain (fluid_synth_t *synth, float gain)
	Set synth output gain value. More...
int	fluid_synth_set_interp_method (fluid_synth_t *synth, int chan, int interp_method)
	Set synthesis interpolation method on one or all MIDI channels. More...
int	fluid_synth_set_polyphony (fluid_synth_t *synth, int polyphony)
	Set synthesizer polyphony (max number of voices). More...
void	fluid_synth_set_sample_rate (fluid_synth_t *synth, float sample_rate)
	Set up an event to change the sample-rate of the synth during the next rendering call. More...

Detailed Description

Functions to control and query synthesis parameters like gain and polyphony count.

Enumeration Type Documentation

fluid_interp

enum fluid_interp

Synthesis interpolation method.

Enumerator
FLUID_INTERP_NONE	No interpolation: Fastest, but questionable audio quality.
FLUID_INTERP_LINEAR	Straight-line interpolation: A bit slower, reasonable audio quality.
FLUID_INTERP_4THORDER	Fourth-order interpolation, best quality, the default.
FLUID_INTERP_7THORDER	Seventh-point sinc interpolation. Note This interpolation method was believed to provide highest quality. However, in Feb. 2025 it was discovered that for certain samples it does introduce ringing artifacts, which are not present in the 4th order interpolation. This is not a bug, it's rather a limitation of only using 7 points for the sinc interpolation.
FLUID_INTERP_DEFAULT	Default interpolation method.
FLUID_INTERP_HIGHEST	Highest interpolation method.

fluid_synth_add_mod

enum fluid_synth_add_mod

Enum used with fluid_synth_add_default_mod() to specify how to handle duplicate modulators.

Enumerator
FLUID_SYNTH_OVERWRITE	Overwrite any existing matching modulator.
FLUID_SYNTH_ADD	Sum up modulator amounts.

Function Documentation

fluid_synth_add_default_mod()

int fluid_synth_add_default_mod	(	fluid_synth_t *	synth,
		const fluid_mod_t *	mod,
		int	mode
	)

Adds the specified modulator mod as default modulator to the synth.

mod will take effect for any subsequently created voice.

Parameters

synth	FluidSynth instance
mod	Modulator info (values copied, passed in object can be freed immediately afterwards)
mode	Determines how to handle an existing identical modulator (fluid_synth_add_mod)

Returns

FLUID_OK on success, FLUID_FAILED otherwise

Note

Not realtime safe (due to internal memory allocation) and therefore should not be called from synthesis context at the risk of stalling audio output.

fluid_synth_count_audio_channels()

int fluid_synth_count_audio_channels

(

fluid_synth_t *

synth

)

Get the total count of audio channels.

Parameters

synth

FluidSynth instance

Returns

Count of audio channel stereo pairs (1 = 2 channels, 2 = 4, etc)

Examples

fluidsynth_process.c.

fluid_synth_count_audio_groups()

int fluid_synth_count_audio_groups

(

fluid_synth_t *

synth

)

Get the total number of allocated audio channels.

Usually identical to the number of audio channels. Can be employed by LADSPA effects subsystem.

Parameters

synth

FluidSynth instance

Returns

Count of audio group stereo pairs (1 = 2 channels, 2 = 4, etc)

fluid_synth_count_effects_channels()

int fluid_synth_count_effects_channels

(

fluid_synth_t *

synth

)

Get the total number of allocated effects channels.

Parameters

synth

FluidSynth instance

Returns

Count of allocated effects channels

Examples

fluidsynth_process.c.

fluid_synth_count_effects_groups()

int fluid_synth_count_effects_groups

(

fluid_synth_t *

synth

)

Get the total number of allocated effects units.

This is the same number as initially provided by the setting synth.effects-groups.

Parameters

synth

FluidSynth instance

Returns

Count of allocated effects units

Examples

fluidsynth_process.c.

fluid_synth_count_midi_channels()

int fluid_synth_count_midi_channels

(

fluid_synth_t *

synth

)

Get the total count of MIDI channels.

Parameters

synth

FluidSynth instance

Returns

Count of MIDI channels

fluid_synth_get_active_voice_count()

int fluid_synth_get_active_voice_count

(

fluid_synth_t *

synth

)

Get current number of active voices.

I.e. the no. of voices that have been started and have not yet finished. Unless called from synthesis context, this number does not necessarily have to be equal to the number of voices currently processed by the DSP loop, see below.

Parameters

synth

FluidSynth instance

Returns

Number of currently active voices.

Since

1.1.0

Note

To generate accurate continuous statistics of the voice count, caller should ensure this function is called synchronously with the audio synthesis process. This can be done in the new_fluid_audio_driver2() audio callback function for example. Otherwise every call to this function may return different voice counts as it may change after any (concurrent) call to fluid_synth_write_*() made by e.g. an audio driver or the applications audio rendering thread.

fluid_synth_get_gain()

float fluid_synth_get_gain

(

fluid_synth_t *

synth

)

Get synth output gain value.

Parameters

synth

FluidSynth instance

Returns

Synth gain value (0.0 to 10.0)

fluid_synth_get_internal_bufsize()

int fluid_synth_get_internal_bufsize

(

fluid_synth_t *

synth

)

Get the internal synthesis buffer size value.

Parameters

synth

FluidSynth instance

Returns

Internal buffer size in audio frames.

Audio is synthesized at this number of frames at a time. Defaults to 64 frames. I.e. the synth can only react to notes, control changes, and other audio affecting events after having processed 64 audio frames.

fluid_synth_get_polyphony()

int fluid_synth_get_polyphony

(

fluid_synth_t *

synth

)

Get current synthesizer polyphony (max number of voices).

Parameters

synth

FluidSynth instance

Returns

Synth polyphony value.

Since

1.0.6

fluid_synth_remove_default_mod()

int fluid_synth_remove_default_mod	(	fluid_synth_t *	synth,
		const fluid_mod_t *	mod
	)

Removes the specified modulator mod from the synth's default modulator list.

fluid_mod_test_identity() will be used to test modulator matching.

Parameters

synth	synth instance
mod	The modulator to remove

Returns

FLUID_OK if a matching modulator was found and successfully removed, FLUID_FAILED otherwise

Note

Not realtime safe (due to internal memory freeing) and therefore should not be called from synthesis context at the risk of stalling audio output.

fluid_synth_set_gain()

void fluid_synth_set_gain	(	fluid_synth_t *	synth,
		float	gain
	)

Set synth output gain value.

Parameters

synth	FluidSynth instance
gain	Gain value (function clamps value to the range 0.0 to 10.0)

fluid_synth_set_interp_method()

int fluid_synth_set_interp_method	(	fluid_synth_t *	synth,
		int	chan,
		int	interp_method
	)

Set synthesis interpolation method on one or all MIDI channels.

Parameters

synth	FluidSynth instance
chan	MIDI channel to set interpolation method on or -1 for all channels
interp_method	Interpolation method (fluid_interp)

Returns

FLUID_OK on success, FLUID_FAILED otherwise

fluid_synth_set_polyphony()

int fluid_synth_set_polyphony	(	fluid_synth_t *	synth,
		int	polyphony
	)

Set synthesizer polyphony (max number of voices).

Parameters

synth	FluidSynth instance
polyphony	Polyphony to assign

Returns

FLUID_OK on success, FLUID_FAILED otherwise

Since

1.0.6

fluid_synth_set_sample_rate()

void fluid_synth_set_sample_rate	(	fluid_synth_t *	synth,
		float	sample_rate
	)

Set up an event to change the sample-rate of the synth during the next rendering call.

Warning

This function is broken-by-design! Don't use it! Starting with fluidsynth 2.4.4 it's a no-op. Instead, specify the sample-rate when creating the synth.

Deprecated:

As of fluidsynth 2.1.0 this function has been deprecated. Changing the sample-rate is generally not considered to be a real-time use-case, as it always produces some audible artifact ("click", "pop") on the dry sound and effects (because LFOs for chorus and reverb need to be reinitialized). The sample-rate change may also require memory allocation deep down in the effect units. However, this memory allocation may fail and there is no way for the caller to know that, because the actual change of the sample-rate is executed during rendering. This function cannot (must not) do the sample-rate change itself, otherwise the synth needs to be locked down, causing rendering to block. Esp. do not use this function if this synth instance is used by an audio driver, because the audio driver cannot be notified by this sample-rate change. Long story short: don't use it.

fluid_synth_t* synth; // assume initialized
// [...]
// sample-rate change needed? Delete the audio driver, if any.
delete_fluid_audio_driver(adriver);
// then delete the synth
delete_fluid_synth(synth);
// update the sample-rate
fluid_settings_setnum(settings, "synth.sample-rate", 22050.0);
// and re-create objects
synth = new_fluid_synth(settings);
adriver = new_fluid_audio_driver(settings, synth);

Parameters

synth	FluidSynth instance
sample_rate	New sample-rate (Hz)

Since

1.1.2