Function fluid_synth_start 

pub unsafe extern "C" fn fluid_synth_start(
    synth: *mut fluid_synth_t,
    id: c_uint,
    preset: *mut fluid_preset_t,
    audio_chan: c_int,
    midi_chan: c_int,
    key: c_int,
    vel: c_int,
) -> c_int

Create and start voices using a preset. The id passed as argument will be used as the voice group id.