fluidsynth/doc/fluidsynth-v10-devdoc.xml

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<article>
  <articleinfo>
    <title>
    FluidSynth 1.0 &mdash; Developer Documentation
    </title>

    <author>
      <firstname>Peter</firstname>
      <surname>Hanappe</surname>
    </author>

    <revhistory>
      <revision>
        <revnumber>1.0</revnumber>
        <date>2003-12-11</date>
        <authorinitials>hanappe</authorinitials>
        <revremark>First attempt.</revremark>
      </revision>
    </revhistory>

    <copyright>
      <year>2003</year>
      <holder>Copyright Peter Hanappe</holder>
    </copyright>

    <legalnotice>
      <para>All the source code examples in this document are in the
      public domain; you can use them as you please. This document is
      licensed under the Creative Commons Attribution License. To view
      a copy of this license, visit
      http://creativecommons.org/licenses/by/1.0/ or send a letter to
      Creative Commons, 559 Nathan Abbott Way, Stanford, California
      94305, USA. The FluidSynth library is distributed under the GNU
      Library General Public License. A copy of the GNU Library
      General Public License is contained in the FluidSynth package;
      if not, write to the Free Foundation, Inc., 59 Temple Place,
      Suite 330, Boston, MA 02111-1307 USA.</para> </legalnotice>

    <keywordset>
      <keyword>FluidSynth</keyword>
      <keyword>software</keyword>
      <keyword>synthesizer</keyword>
      <keyword>SoundFont</keyword>
      <keyword>Linux</keyword>
      <keyword>audio</keyword>
      <keyword>development</keyword>
      <keyword>documentation</keyword>
      <keyword>HOWTO</keyword>
    </keywordset>

    <abstract>

      <para>FluidSynth is a software synthesizer based on the
      SoundFont 2 specifications. The synthesizer is available as a
      shared object that can easily be reused in any application that
      wants to use wavetable synthesis. This documents explains the
      basic usage of FluidSynth. Some of the more advanced features
      are not yet discussed but will be added in future
      versions.</para>

    </abstract>
  </articleinfo> 

  <sect1>
    <title>Disclaimer</title>

    <para>This documentation, in its current version, is probably
    outdated and most certainly incomplete. As always, the source code
    is the final reference.</para>

    <para>SoundFont(R) is a registered trademark of E-mu Systems, Inc.</para>

  </sect1>

  <sect1>
    <title>Introduction</title>

    <para>FluidSynth can easily be embedded in an application. It has
    a main header file, fluidsynth.h, and one dynamically linkable
    library. FluidSynth runs on Linux, MacOS 9, MacOS X, and the Win32
    platforms. It has audio and midi drivers for all mentioned
    platforms but you can use it with your own drivers if your
    application already handles audio and MIDI input/output. This
    document explains the basic usage of FluidSynth and provides
    examples that you can reuse. </para>

  </sect1>


  <sect1>
    <title>Creating and changing the settings</title>

    <para>
    Before you can use the synthesizer, you have to create a settings
    object. The settings objects is used by all components of the
    FluidSynth library. It gives a unified API to set the parameters
    of the audio drivers, the midi drivers, the synthesizer,
    andsoforth. A number of default settings are defined by the
    current implementation. In future versions, the use of the
    settings will probably be generalized.</para>
 
    <para>
    All settings have a name that follows the "dotted-name"
    notation. For example, "synth.polyphony" refers to the number of
    voices (polyphony) preallocated 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 <function>fluid_settings_setstr</function>,
    <function>fluid_settings_setnum</function>, and
    <function>fluid_settings_setint</function> functions. For example:

<programlisting>
#include &lt;fluidsynth.h&gt;

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;
}
</programlisting>

    </para>

    <para>
    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 minumum 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 on a logarithmic
    scale. Check the API documentation for a description of all
    functions.
    </para>

  </sect1>

  <sect1>
    <title>Creating the synthesizer</title>

    <para>
    To create the synthesizer, you pass it the settings object, as
    in the following example:

<programlisting>
#include &lt;fluidsynth.h&gt;

int main(int argc, char** argv) 
{
  fluid_settings_t* settings;
  fluid_synth_t* synth;

  fluid_settings_t* settings = new_fluid_settings();

  synth = new_fluid_synth(settings);

  /* Do useful things here */

  delete_fluid_synth(synth);
  delete_fluid_settings(settings);
  return 0;
}
</programlisting>
    </para>

    <para>
    The default settings should be fine for most uses. A detailed
    description of all the settings used by the synthesizer described
    below.

<table frame="all"><title>Synthesizer settings</title>
<tgroup cols="3" colsep="0" rowsep="0" align="left">
<tbody>

<!-- separation line -->
<row>
  <entry>synth.gain</entry>
  <entry>Type</entry>
  <entry>number</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>0.2</entry>
</row>
<row>
  <entry></entry>
  <entry>Min-Max</entry>
  <entry>0.0-10.0</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry>The gain is applied to the final or master output of the
synthesizer. It is set to a low value by default to avoid the
saturation of the output when random MIDI files are played.</entry>
</row>

<!-- separation line -->
<row>
  <entry>synth.sample-rate</entry>
  <entry>Type</entry>
  <entry>number</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>44100</entry>
</row>
<row>
  <entry></entry>
  <entry>Min-Max</entry>
  <entry>22050-96000</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry>The sample rate of the audio generated by the synthesizer.</entry>
</row>

<!-- separation line -->
<row>
  <entry>synth.polyphony</entry>
  <entry>Type</entry>
  <entry>integer</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>256</entry>
</row>
<row>
  <entry></entry>
  <entry>Min-Max</entry>
  <entry>16-4096</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry>The polyphony defines how many voices can be played in parallel. The
number of voices is not necessarily equivalent to the number of notes
played simultaniously. Indeed, when a note is struck on a specific
MIDI channel, the preset on that channel may created several voices,
for example, one for the left audio channel and one for the right
audio channels. The number of voices activated depends on the number
of instrument zones that fall in the correspond to the velocity and
key of the played note.</entry>
</row>

<!-- separation line -->
<row>
  <entry>synth.midi-channels</entry>
  <entry>Type</entry>
  <entry>integer</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>16</entry>
</row>
<row>
  <entry></entry>
  <entry>Min-Max</entry>
  <entry>16-256</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry>This setting defines the number of MIDI channels of the
synthesizer. The MIDI standard defines 16 channels, so most hardware
keyboards are limited to 16. If you plan to use the synthesizer as a
plugin in an application, it might be interesting to set the number of
channels to a larger value. In this case you can program a greater
number of presets.</entry>
</row>

<!-- separation line -->
<row>
  <entry>synth.reverb.active</entry>
  <entry>Type</entry>
  <entry>string</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>"yes"</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry>When set to "yes" the reverb effects module is activated. Otherwise,
no reverb will be added to the output signal. Note that when the
reverb module is active, the amount of signal send to the reverb
module depends on the "reverb send" generator defined in the
SoundFont.</entry>
</row>

<!-- separation line -->
<row>
  <entry>synth.chorus.active</entry>
  <entry>Type</entry>
  <entry>string</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>"yes"</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry>When set to "yes" the chorus effects module is activated. Otherwise,
no chorus will be added to the output signal. Note that when the
reverb module is active, the amount of signal send to the chorus
module depends on the "chorus send" generator defined in the
SoundFont.</entry>
</row>

<!-- separation line -->
<row>
  <entry>synth.ladspa.active</entry>
  <entry>Type</entry>
  <entry>string</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>"no"</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry>When set to "yes" the LADSPA subsystem will be called. This subsystem
allows to load and interconnect LADSPA plugins. The output of the
synthesizer is processed by the LADSPA subsystem. Note that the
synthesizer has to be compiled with LADSPA support. More information
about the LADSPA subsystem later.</entry>
</row>

<!-- separation line -->
<row>
  <entry>synth.audio-groups</entry>
  <entry>Type</entry>
  <entry>integer</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>1</entry>
</row>
<row>
  <entry></entry>
  <entry>Min-Max</entry>
  <entry>1-128</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry>By default, the synthesizer outputs a single stereo signal. Using this
option, the synthesizer can output multichannel audio.</entry>
</row>

<!-- separation line -->
<row>
  <entry>synth.effects-channels</entry>
  <entry>Type</entry>
  <entry>integer</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>2</entry>
</row>
<row>
  <entry></entry>
  <entry>Min-Max</entry>
  <entry>2-2</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry></entry>
</row>

<!-- separation line -->
<row>
  <entry>synth.verbose</entry>
  <entry>Type</entry>
  <entry>string</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>"no"</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>

  <entry>When set to "yes" the synthesizer will print out information
  about the received MIDI events to the stdout. This can be helpful
  for debugging. This setting can not be changed after the synthesizer
  has started.</entry>

</row>

<!-- separation line -->
<row>
  <entry>synth.dump</entry>
  <entry>Type</entry>
  <entry>string</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>"no"</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry></entry>
</row>

</tbody>
</tgroup>
</table>


    </para>
  </sect1>

  <sect1>
    <title>Creating the audio driver</title>

    <para>
    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.
    </para>

    <para>
    Creating the audio driver is straightforward: set the appropriate
    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 theaudio systems that
    are currently supported. It displays the name, as used by the
    fluidsynth library, and a description. </para>

    <para>
    <itemizedlist>
      <listitem><para>alsa: Advanced Linux Sound Architecture</para></listitem>
      <listitem><para>oss: Open Sound System (Linux)</para></listitem>
      <listitem><para>jack: JACK Audio Connection Kit (Linux, Mac OS X)</para></listitem>
      <listitem><para>portaudio: Portaudio Library (MacOS 9 &amp; X, Windows, Linux)</para></listitem>
      <listitem><para>sndmgr: Apple SoundManager (Mac OS Classic)</para></listitem>
      <listitem><para>coreaudio: Apple CoreAudio (MacOS X, experimental)</para></listitem>
      <listitem><para>dsound: Microsoft DirectSound (Windows)</para></listitem>
    </itemizedlist>
    </para>

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

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

    <para>
    You create the audio driver with the
    <function>new_fluid_audio_driver</function> function. This
    function takes the settings and synthesizer object as
    arguments. For example:

<programlisting>
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);
}
</programlisting>
    </para>

    <para>
    As soon as the audio driver is created, it will start playing. The
    audio driver creates a separate thread that runs in real-time mode
    (is the application has sufficient privileges) and call the
    synthesizer object to generate the audio.
    </para>


    <para>
    There are a number of general audio driver settings. The
    audio.driver settings defines 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. They will be
    documented later.  
    </para>

<table frame="all"><title>General audio driver settings</title>
<tgroup cols="3" align="left" colsep="0" rowsep="0">
<tbody>

<!-- separation line -->
<row>
  <entry>audio.driver</entry>
  <entry>Type</entry>
  <entry>string</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>alsa (Linux), dsound (Windows), sndman (MacOS9), coreaudio (MacOS X)</entry>
</row>
<row>
  <entry></entry>
  <entry>Options</entry>
  <entry>alsa, oss, jack, dsound, sndman, coreaudio, portaudio</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry>The audio system to be used.</entry>
</row>

<!-- separation line -->
<row>
  <entry>audio.periods</entry>
  <entry>Type</entry>
  <entry>int</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>16 (Linux, MacOS X), 8 (Windows)</entry>
</row>
<row>
  <entry></entry>
  <entry>Min-Max</entry>
  <entry>2-64</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry>The number of the audio buffers used by the driver. This
  number of buffers, multiplied by the buffer size (see setting
  audio.period-size), determines the maximum latency of the audio
  driver.</entry>
</row>

<!-- separation line -->
<row>
  <entry>audio.period-size</entry>
  <entry>Type</entry>
  <entry>int</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>64 (Linux, MacOS X), 512 (Windows)</entry>
</row>
<row>
  <entry></entry>
  <entry>Min-Max</entry>
  <entry>64-8192</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>
  <entry>The size of the audio buffers (in frames).</entry>
</row>

<!-- separation line -->
<row>
  <entry>audio.sample-format</entry>
  <entry>Type</entry>
  <entry>string</entry>
</row>
<row>
  <entry></entry>
  <entry>Default</entry>
  <entry>"16bits"</entry>
</row>
<row>
  <entry></entry>
  <entry>Options</entry>
  <entry>"16bits", "float"</entry>
</row>
<row>
  <entry></entry>
  <entry>Description</entry>

  <entry>The format of the audio samples. This is currently only an
  indication; the audio driver may ignore this setting if it can't
  handle the specified format.</entry>

</row>

</tbody>
</tgroup>
</table>


  </sect1>

  <sect1>
    <title>Using the synthesizer without an audio driver</title>

    <para>
    It is possible to use the synthesizer object without creating an
    audio driver. This is desirable if the application using
    FluidSynth manages the audio output itself. The synthesizer has
    several API functions that can be used to obtain the audio output:
    </para>

    <para>
    <function>fluid_synth_write_s16</function> fills two buffers (left
    and right channel) with samples coded as signed 16 bits (the
    endian-ness is machine
    dependent). <function>fluid_synth_write_float</function> fills a
    left and right audio buffer with 32 bits floating point
    samples. For multi channel audio output, the function
    <function>fluid_synth_nwrite_float</function> has to be used.
    </para>

    <para>
    The function <function>fluid_synth_process</function> is still
    experimental and its use is therefore not recommended but it will
    probably become the generic interface in future versions.  
    </para>

  </sect1>

  <sect1>
    <title>Loading and managing SoundFonts</title>

    <para>
    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.
    </para>

    <para>
    SoundFonts are loaded with the
    <function>fluid_synth_sfload</function> 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.
    </para>

    <para>
    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
    (<function>fluid_synth_program_select</function>). This function
    is not invokeable through MIDI messages, though.  
    </para>

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

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

    <para>
    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
    <function>fluid_synth_sfload</function> and
    <function>fluid_synth_sfunload</function> functions should be set
    to zero.  
    </para>

  </sect1>

  <sect1>
    <title>Sending MIDI events</title>

    <para>
    Once the synthesizer is up and running and a SoundFont is loaded,
    most people will want to do something usefull with it. Make noise,
    for example. The synthesizer aims to be compatible with the MIDI
    standard, so it accepts almost all MIDI messages (details on the
    MIDI compatibility elsewhere). The MIDI channel messages can be
    send using the <function>fluid_synth_noteon</function>,
    <function>fluid_synth_noteoff</function>,
    <function>fluid_synth_cc</function>,
    <function>fluid_synth_pitch_bend</function>,
    <function>fluid_synth_pitch_wheel_sens</function>, and
    <function>fluid_synth_program_change</function> functions. For
    convenience, there's also a
    <function>fluid_synth_bank_select</function> function (the bank
    select message is normally sent using a control change message).
    </para>

    <para>
    The following example show a generic graphical button that plays a
    not when clicked:

<programlisting>
class SoundButton : public SomeButton
{
public:	
  
  SoundButton() : SomeButton() {
    if (!_synth) {
       initSynth();
    }
  }

  static void initSynth() {
    _settings = new_fluid_settings();
    _synth = new_fluid_synth(_settings);
    _adriver = new_fluid_audio_driver(_settings, _synth);
  }

  /* ... */

  virtual int handleMouseDown(int x, int y) {
    /* Play a note on key 60 with velocity 100 on MIDI channel 0 */
    fluid_synth_noteon(_synth, 0, 60, 100);
  }

  virtual int handleMouseUp(int x, int y) {
    /* Release the note on key 60 */
    fluid_synth_noteoff(_synth, 0, 60);
  }


protected:

  static fluid_settings_t* _settings;
  static fluid_synth_t* _synth;
  static fluid_audio_driver_t* _adriver;
};
</programlisting>
    </para>


  </sect1>

  <sect1>
    <title>Advanced features, not yet documented</title>

<itemizedlist mark="opencircle">
<listitem><para>Accessing low-level voice parameters</para></listitem>
<listitem><para>Reverb settings</para></listitem>
<listitem><para>Chorus settings</para></listitem>
<listitem><para>Interpolation settings (set_gen, get_gen, NRPN)</para></listitem>
<listitem><para>Sequencer</para></listitem>
<listitem><para>LADSPA effects unit</para></listitem>
<listitem><para>MIDI router</para></listitem>
<listitem><para>Multi-channel audio</para></listitem>
<listitem><para>MIDI tunings</para></listitem>
<listitem><para>MIDI file player</para></listitem>
<listitem><para>SoundFont loader</para></listitem>
</itemizedlist>

  </sect1>
</article>