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)
• wasapi: Windows Audio Session API (Windows Vista and later)
• 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)
• 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)
• sdl3*: Simple DirectMedia Layer (Linux, Windows, Mac OS X, iOS, Android, FreeBSD, Haiku, etc.)
• pipewire**: PipeWire (Linux)
• file: Driver to output audio to a file

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 audio driver options that define the audio quality and latency include audio.sample-format, audio.period-size, and audio.periods. The synthesizer's synth.sample-rate is also involved. The details are described later.

Important: Configure the synthesizer before creating the audio driver. In particular, set synth.sample-rate before instantiating the synth with new_fluid_synth(). After the synth has been created, changing synth.sample-rate in the settings object may not change the sample rate used by the synthesizer, while audio drivers created later may use the updated setting value and cause the audio to be played 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.

You can 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 receives audio samples from the synthesizer object and transfers them to an audio endpoint to generate sound.

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 sdl3 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. A warning may be printed if sdl3 is available, but no such call has been made.

**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.

Warnings raised by audio drivers during initialization via new_fluid_settings() can be suppressed by disabling those audio drivers with fluid_audio_driver_register().