Make Fine Tune destination of default modulator Pitch-Wheel-To-pitch (#590)

include/fluidsynth/gen.h

@@ -95,11 +95,22 @@ enum fluid_gen_type
     GEN_EXCLUSIVECLASS,		/**< Exclusive class number */
     GEN_OVERRIDEROOTKEY,		/**< Sample root note override */
 
-    /* the initial pitch is not a "standard" generator. It is not
-     * mentioned in the list of generator in the SF2 specifications. It
-     * is used, however, as the destination for the default pitch wheel
-     * modulator. */
-    GEN_PITCH,			/**< Pitch @note Not a real SoundFont generator */
+    /**
+     * @brief Initial Pitch
+     *
+     * @note This is not "standard" SoundFont generator, because it is not
+     * mentioned in the list of generators in the SF2 specifications.
+     * It is used by FluidSynth internally to compute the nominal pitch of
+     * a note on note-on event. By nature it shouldn't be allowed to be modulated,
+     * however the specification defines a default modulator having "Initial Pitch"
+     * as destination (cf. SF2.01 page 57 section 8.4.10 MIDI Pitch Wheel to Initial Pitch).
+     * Thus it is impossible to cancel this default modulator, which would be required
+     * to let the MIDI Pitch Wheel controller modulate a different generator.
+     * In order to provide this flexibility, FluidSynth >= 2.1.0 uses a default modulator
+     * "Pitch Wheel to Fine Tune", rather than Initial Pitch. The same "compromise" can
+     * be found on the Audigy 2 ZS for instance.
+     */
+    GEN_PITCH,
 
     GEN_CUSTOM_BALANCE,          /**< Balance @note Not a real SoundFont generator */
     /* non-standard generator for an additional custom high- or low-pass filter */

src/synth/fluid_gen.c

@@ -26,7 +26,7 @@
 /* See SFSpec21 $8.1.3 */
 static const fluid_gen_info_t fluid_gen_info[] =
 {
-    /* number/name             init  scale         min        max         def */
+    /* number/name             init  nrpn-scale    min        max         def */
     { GEN_STARTADDROFS,           1,     1,       0.0f,     1e10f,       0.0f },
     { GEN_ENDADDROFS,             1,     1,     -1e10f,      0.0f,       0.0f },
     { GEN_STARTLOOPADDROFS,       1,     1,     -1e10f,     1e10f,       0.0f },

src/synth/fluid_gen.h

@@ -27,7 +27,7 @@
 typedef struct _fluid_gen_info_t
 {
     char num;		/* Generator number */
-    char init;		/* Does the generator need to be initialized (cfr. fluid_voice_init()) */
+    char init;		/* Does the generator need to be initialized (not used) */
     char nrpn_scale;	/* The scale to convert from NRPN (cfr. fluid_gen_map_nrpn()) */
     float min;		/* The minimum value */
     float max;		/* The maximum value */

src/synth/fluid_synth.c

@@ -431,6 +431,10 @@ fluid_synth_init(void)
 
 
     /* SF2.01 page 57 section 8.4.10 MIDI Pitch Wheel to Initial Pitch ... */
+    /* Initial Pitch is not a "standard" generator, because it isn't mentioned in the
+       list of generators in the SF2 specifications. That's why destination Initial Pitch
+       is replaced here by fine tune generator.
+     */
     fluid_mod_set_source1(&default_pitch_bend_mod, FLUID_MOD_PITCHWHEEL, /* Index=14 */
                           FLUID_MOD_GC                              /* CC =0 */
                           | FLUID_MOD_LINEAR                        /* type=0 */
@@ -443,7 +447,8 @@ fluid_synth_init(void)
                           | FLUID_MOD_UNIPOLAR                                /* P=0 */
                           | FLUID_MOD_POSITIVE                                /* D=0 */
                          );
-    fluid_mod_set_dest(&default_pitch_bend_mod, GEN_PITCH);                 /* Destination: Initial pitch */
+    /* Also see the comment in gen.h about GEN_PITCH */
+    fluid_mod_set_dest(&default_pitch_bend_mod, GEN_FINETUNE);              /* Destination: Fine Tune */
     fluid_mod_set_amount(&default_pitch_bend_mod, 12700.0);                 /* Amount: 12700 cents */