Creating the audio driver

The synthesizer itself does not write any audio to the audio output. This allows application developers to manage the audio output themselves if they wish. The next section describes the use of the synthesizer without an audio driver in more detail.

Creating the audio driver is straightforward: set the audio.driver settings and create the driver object. Because the FluidSynth has support for several audio systems, you may want to change which one you want to use. The list below shows the audio systems that are currently supported. It displays the name, as used by the fluidsynth library, and a description.

• jack: JACK Audio Connection Kit (Linux, Mac OS X, Windows)
• alsa: Advanced Linux Sound Architecture (Linux)
• oss: Open Sound System (primarily needed on BSD, rarely also Linux and Unix in general)
• pulseaudio: PulseAudio (Linux, Mac OS X, Windows)
• coreaudio: Apple CoreAudio (Mac OS X)
• dsound: Microsoft DirectSound (Windows)
• portaudio: PortAudio Library (Mac OS 9 & X, Windows, Linux)
• sndman: Apple SoundManager (Mac OS Classic)
• dart: DART sound driver (OS/2)
• opensles: OpenSL ES (Android)
• oboe: Oboe (Android)
• waveout: Microsoft WaveOut, alternative to DirectSound (Windows CE x86, Windows Mobile 2003 for ARMv5, Windows 98 SE, Windows NT 4.0, Windows XP and later)
• file: Driver to output audio to a file
• sdl2*: Simple DirectMedia Layer (Linux, Windows, Mac OS X, iOS, Android, FreeBSD, Haiku, etc.)
• pipewire**: PipeWire (Linux)

The default audio driver depends on the settings with which FluidSynth was compiled. You can get the default driver with fluid_settings_getstr_default(). To get the list of available drivers use the fluid_settings_foreach_option() function. Finally, you can set the driver with fluid_settings_setstr(). In most cases, the default driver should work out of the box.

Additional options that define the audio quality and latency are audio.sample-format, audio.period-size, and audio.periods. The details are described later.

You create the audio driver with the new_fluid_audio_driver() function. This function takes the settings and synthesizer object as arguments. For example:

void init() 
{
    fluid_settings_t* settings;
    fluid_synth_t* synth;
    fluid_audio_driver_t* adriver;
    settings = new_fluid_settings();
 
    /* Set the synthesizer settings, if necessary */
    synth = new_fluid_synth(settings);
 
    fluid_settings_setstr(settings, "audio.driver", "jack");
    adriver = new_fluid_audio_driver(settings, synth);
}

As soon as the audio driver is created, it will start playing. The audio driver creates a separate thread that uses the synthesizer object to generate the audio.

There are a number of general audio driver settings. The audio.driver settings define the audio subsystem that will be used. The audio.periods and audio.period-size settings define the latency and robustness against scheduling delays. There are additional settings for the audio subsystems used. For a full list of available audio driver settings, please refer to the Audio driver settings documentation.

*Note: In order to use sdl2 as audio driver, the application is responsible for initializing SDL (e.g. with SDL_Init()). This must be done before the first call to new_fluid_settings()! Also make sure to call SDL_Quit() after all fluidsynth instances have been destroyed.

**Note: In order to use pipeiwre as audio driver, the application is responsible for initializing PipeWire (e.g. with pw_init()). This must be done before the first call to new_fluid_settings()! Also make sure to call pw_deinit() after all fluidsynth instances have been destroyed.