Before you can use the synthesizer, you have to create a settings object. The settings objects is used by many components of the FluidSynth library. It gives a unified API to set the parameters of the audio drivers, the midi drivers, the synthesizer, and so forth. A number of default settings are defined by the current implementation.

All settings have a name that follows the "dotted-name" notation. For example, synth.polyphony refers to the number of voices (polyphony) allocated by the synthesizer. The settings also have a type. There are currently three types: strings, numbers (double floats), and integers. You can change the values of a setting using the fluid_settings_setstr(), fluid_settings_setnum(), and fluid_settings_setint() functions. For example:

#include <fluidsynth.h>
 
int main(int argc, char** argv) 
{
    fluid_settings_t* settings = new_fluid_settings();
    fluid_settings_setint(settings, "synth.polyphony", 128);
    /* ... */
    delete_fluid_settings(settings);
    return 0;
}

The API contains the functions to query the type, the current value, the default value, the range and the "hints" of a setting. The range is the minimum and maximum value of the setting. The hints gives additional information about a setting. For example, whether a string represents a filename. Or whether a number should be interpreted on a logarithmic scale. Check the settings.h API documentation for a description of all functions.