Chorus enhancement. (#548)

This adds new LFO modulators:
 - these modulators are computed on the fly, instead of using lfo lookup table. Advantages:
      - Avoiding a lost of 608272 memory bytes when lfo speed is low (0.3Hz).
      - Allows to diminish the lfo speed lower limit to 0.1Hz instead of 0.3Hz.
        A speed of 0.1 is interesting for chorus. Using a lookup table for 0.1Hz
        would require too much memory (1824816 bytes).
      - Make use of first-order all-pass interpolator instead of bandlimited interpolation.
      - Although lfo modulator is computed on the fly, cpu load is lower than using
        lfo lookup table with bandlimited interpolator.

Also adds a stereo unit controlled by WIDTH macro. WIDTH [0..10] value define a stereo separation between left and right.
 - When 0, the output is monophonic.
 - When > 0 , the output is stereophonic.

 WIDTH is currently fixed to maximum value to provide maximum stereo effect.

doc/fluidsettings.xml

@@ -73,7 +73,7 @@ Developers: Settings can be deprecated by adding: <deprecated>SOME TEXT</depreca
             <name>chorus.speed</name>
             <type>num</type>
             <def>0.3</def>
-            <min>0.29</min>
+            <min>0.1</min>
             <max>5</max>
             <desc>
                 Sets the modulation speed in Hz.</desc>

doc/fluidsynth-v20-devdoc.txt

@@ -21,6 +21,7 @@ All the source code examples in this document are in the public domain; you can
 
 - \ref Disclaimer
 - \ref Introduction
+- \ref NewIn2_1_0
 - \ref NewIn2_0_7
 - \ref NewIn2_0_6
 - \ref NewIn2_0_5
@@ -65,6 +66,9 @@ What is FluidSynth?
 
 - FluidSynth is open source, in active development. For more details, take a look at http://www.fluidsynth.org
 
+\section NewIn2_1_0 Whats new in 2.1.0?
+
+- smallest allowed chorus speed is now 0.1 Hz (previously 0.29 Hz)
 
 \section NewIn2_0_7 Whats new in 2.0.7?
 

src/rvoice/fluid_chorus.h

@@ -49,7 +49,6 @@ typedef enum
  */
 fluid_chorus_t *new_fluid_chorus(fluid_real_t sample_rate);
 void delete_fluid_chorus(fluid_chorus_t *chorus);
-int fluid_chorus_init(fluid_chorus_t *chorus);
 void fluid_chorus_reset(fluid_chorus_t *chorus);
 
 void fluid_chorus_set(fluid_chorus_t *chorus, int set, int nr, fluid_real_t level,

src/synth/fluid_synth.c

@@ -198,7 +198,7 @@ void fluid_synth_settings(fluid_settings_t *settings)
     fluid_settings_register_int(settings, "synth.chorus.active", 1, 0, 1, FLUID_HINT_TOGGLED);
     fluid_settings_register_int(settings, "synth.chorus.nr", FLUID_CHORUS_DEFAULT_N, 0, 99, 0);
     fluid_settings_register_num(settings, "synth.chorus.level", FLUID_CHORUS_DEFAULT_LEVEL, 0.0f, 10.0f, 0);
-    fluid_settings_register_num(settings, "synth.chorus.speed", FLUID_CHORUS_DEFAULT_SPEED, 0.29f, 5.0f, 0);
+    fluid_settings_register_num(settings, "synth.chorus.speed", FLUID_CHORUS_DEFAULT_SPEED, 0.1f, 5.0f, 0);
     fluid_settings_register_num(settings, "synth.chorus.depth", FLUID_CHORUS_DEFAULT_DEPTH, 0.0f, 256.0f, 0);
 
     fluid_settings_register_int(settings, "synth.ladspa.active", 0, 0, 1, FLUID_HINT_TOGGLED);
@@ -5272,7 +5272,7 @@ fluid_synth_set_chorus_on(fluid_synth_t *synth, int on)
  * @param nr Chorus voice count (0-99, CPU time consumption proportional to
  *   this value)
  * @param level Chorus level (0.0-10.0)
- * @param speed Chorus speed in Hz (0.29-5.0)
+ * @param speed Chorus speed in Hz (0.1-5.0)
  * @param depth_ms Chorus depth (max value depends on synth sample rate,
  *   0.0-21.0 is safe for sample rate values up to 96KHz)
  * @param type Chorus waveform type (#fluid_chorus_mod)
@@ -5330,19 +5330,6 @@ int fluid_synth_set_chorus_type(fluid_synth_t *synth, int type)
     return fluid_synth_set_chorus_full(synth, FLUID_CHORUS_SET_TYPE, 0, 0, 0, 0, type);
 }
 
-/**
- * Set one or more chorus parameters.
- * @param synth FluidSynth instance
- * @param set Flags indicating which chorus parameters to set (#fluid_chorus_set_t)
- * @param nr Chorus voice count (0-99, CPU time consumption proportional to
- *   this value)
- * @param level Chorus level (0.0-10.0)
- * @param speed Chorus speed in Hz (0.29-5.0)
- * @param depth_ms Chorus depth (max value depends on synth sample rate,
- *   0.0-21.0 is safe for sample rate values up to 96KHz)
- * @param type Chorus waveform type (#fluid_chorus_mod)
- * @return #FLUID_OK on success, #FLUID_FAILED otherwise
- */
 int
 fluid_synth_set_chorus_full(fluid_synth_t *synth, int set, int nr, double level,
                             double speed, double depth_ms, int type)
@@ -5399,7 +5386,7 @@ fluid_synth_set_chorus_full(fluid_synth_t *synth, int set, int nr, double level,
 /**
  * Get chorus voice number (delay line count) value.
  * @param synth FluidSynth instance
- * @return Chorus voice count (0-99)
+ * @return Chorus voice count
  */
 int
 fluid_synth_get_chorus_nr(fluid_synth_t *synth)
@@ -5415,7 +5402,7 @@ fluid_synth_get_chorus_nr(fluid_synth_t *synth)
 /**
  * Get chorus level.
  * @param synth FluidSynth instance
- * @return Chorus level value (0.0-10.0)
+ * @return Chorus level value
  */
 double
 fluid_synth_get_chorus_level(fluid_synth_t *synth)
@@ -5431,7 +5418,7 @@ fluid_synth_get_chorus_level(fluid_synth_t *synth)
 /**
  * Get chorus speed in Hz.
  * @param synth FluidSynth instance
- * @return Chorus speed in Hz (0.29-5.0)
+ * @return Chorus speed in Hz
  */
 double
 fluid_synth_get_chorus_speed(fluid_synth_t *synth)