Loading and managing SoundFonts
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## Loading and managing SoundFonts

Before any sound can be produced, the synthesizer needs a SoundFont. For a discussion on SoundFont please refer to some other, not yet existing, therefore virtual document.

SoundFonts are loaded with the `fluid_synth_sfload` function. The function takes the path to a SoundFont file as argument and a boolean to indicate whether the presets of the MIDI channels should be updated after the SoundFont is loaded. More on the preset updates below.

The synthesizer can load any number of SoundFonts. This is an advantage, of course, but there are some issues that you must be aware of. The presets in a SoundFont are identified by their bank and preset number. The MIDI specifications allows the change of a preset on a MIDI channel using the combination of "bank select" and the "program change" messages. An ambiguity arrizes when a preset with a specific bank and preset number is defined in multiple loaded SoundFonts. This is solved by searching the SoundFonts in the inverse order they were loaded, i.e. the lastly loaded SoundFont is searched first for the request preset (identified by bank and preset number) then the on but last loaded SoundFont, and so on until. The first preset found is then used. You can somehow consider the SoundFonts placed on a stack. The SoundFont on top of the stack is inspected first, followed by the SoundFont down on the stack. Newly loaded SoundFonts are always placed on top of the stack. This is how commercial, hardware synthesizers work. The inconvenience is that a preset in a SoundFont at the bottom end of the stack may be masked by a preset in a SoundFont at the top of the stack. Using the standard MIDI messages, bank select and program change, there is no way to select a masked preset. However, FluidSynth has an API function to unambiguously select a preset (`fluid_synth_program_select`). This function is not invokeable through MIDI messages, though.

The `fluid_synth_sfload` function returns the unique identifier of the loaded SoundFont, or -1 in case of an error. This identifier is used in subsequent management functions: `fluid_synth_sfunload` removes the SoundFont, `fluid_synth_sfreload` reloads the SoundFont. When a SoundFont is reloaded, it retains it's ID and position on the SoundFont stack.

Additional API functions are provided to get the number of loaded SoundFonts ot to get a pointer to the SoundFont.

Another issue that needs some explanation is the reprogramming of the presets after a SoundFont load or unload. The default behavior of commercial synthesizers is to reset all the preset that are programmed on the MIDI channels when a SoundFont is loaded or unloaded. Consider the case where MIDI channel 1 uses preset (0, 0) (the couple indicates the bank and program number). This preset was found in the SoundFont with ID 3, for example. When a new SoundFont is loaded that also contains a preset with bank number 0 and program number 0, then the newly loaded preset will be used on channel 1 for future events. This behavior is as if a bank select and program change message is send to all channels after a load/unload using the channel's bank and program number. This may be sometimes confusing or unwanted. A user may not want to loose its preset setup when a new SoundFont is loaded. To avoid the reprogramming of the presets, the third parameter to the `fluid_synth_sfload` and `fluid_synth_sfunload` functions should be set to zero.

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