Select soundfont samples by frequency instead of midi note numbers (#932)

For detuned channels it might be better to use another key for Soundfont sample selection
giving better approximations for the pitch than the original key.
Example: play key 60 on 6370 Hz => use tuned key 64 for sample selection

This feature is only enabled for melodic channels.
For drum channels we always select Soundfont samples by key numbers.

AUTHORS

@@ -151,3 +151,4 @@ Sven Meier
 Marcus Weseloh
 Jean-jacques Ceresa
 Vladimir Davidovich
+Tamás Korodi

src/sfloader/fluid_defsfont.c

@@ -27,6 +27,7 @@
 #include "fluid_sys.h"
 #include "fluid_synth.h"
 #include "fluid_samplecache.h"
+#include "fluid_chan.h"
 
 /* EMU8k/10k hardware applies this factor to initial attenuation generator values set at preset and
  * instrument level in a soundfont. We apply this factor when loading the generator values to stay
@@ -867,8 +868,26 @@ fluid_defpreset_noteon(fluid_defpreset_t *defpreset, fluid_synth_t *synth, int c
     fluid_voice_zone_t *voice_zone;
     fluid_list_t *list;
     fluid_voice_t *voice;
+    int tuned_key;
     int i;
 
+    /* For detuned channels it might be better to use another key for Soundfont sample selection
+     * giving better approximations for the pitch than the original key.
+     * Example: play key 60 on 6370 Hz => use tuned key 64 for sample selection
+     *
+     * This feature is only enabled for melodic channels.
+     * For drum channels we always select Soundfont samples by key numbers.
+     */
+
+    if(synth->channel[chan]->channel_type == CHANNEL_TYPE_MELODIC)
+    {
+        tuned_key = (int)(fluid_channel_get_key_pitch(synth->channel[chan], key) / 100.0f + 0.5f);
+    }
+    else
+    {
+        tuned_key = key;
+    }
+
     global_preset_zone = fluid_defpreset_get_global_zone(defpreset);
 
     /* run thru all the zones of this preset */
@@ -879,7 +898,7 @@ fluid_defpreset_noteon(fluid_defpreset_t *defpreset, fluid_synth_t *synth, int c
 
         /* check if the note falls into the key and velocity range of this
            preset */
-        if(fluid_zone_inside_range(&preset_zone->range, key, vel))
+        if(fluid_zone_inside_range(&preset_zone->range, tuned_key, vel))
         {
 
             inst = fluid_preset_zone_get_inst(preset_zone);
@@ -894,7 +913,7 @@ fluid_defpreset_noteon(fluid_defpreset_t *defpreset, fluid_synth_t *synth, int c
                    the key and velocity range of this  instrument zone.
                    An instrument zone must be ignored when its voice is already running
                    played by a legato passage (see fluid_synth_noteon_monopoly_legato()) */
-                if(fluid_zone_inside_range(&voice_zone->range, key, vel))
+                if(fluid_zone_inside_range(&voice_zone->range, tuned_key, vel))
                 {
 
                     inst_zone = voice_zone->inst_zone;

src/synth/fluid_chan.c

@@ -374,6 +374,27 @@ fluid_channel_get_sfont_bank_prog(fluid_channel_t *chan, int *sfont,
     }
 }
 
+/**
+ * Compute the pitch for a key after applying Fluidsynth's tuning functionality
+ * and channel coarse/fine tunings.
+ * @param chan fluid_channel_t
+ * @param key MIDI note number (0-127)
+ * @return the pitch of the key
+ */
+fluid_real_t fluid_channel_get_key_pitch(fluid_channel_t *chan, int key)
+{
+    if(chan->tuning)
+    {
+        return fluid_tuning_get_pitch(chan->tuning, key)
+            + 100.0f * fluid_channel_get_gen(chan, GEN_COARSETUNE)
+            + fluid_channel_get_gen(chan, GEN_FINETUNE);
+    }
+    else
+    {
+        return key * 100.0f;
+    }
+}
+
 /**
  * Updates legato/ staccato playing state
  * The function is called:

src/synth/fluid_chan.h

@@ -142,6 +142,7 @@ void fluid_channel_set_bank_lsb(fluid_channel_t *chan, int banklsb);
 void fluid_channel_set_bank_msb(fluid_channel_t *chan, int bankmsb);
 void fluid_channel_get_sfont_bank_prog(fluid_channel_t *chan, int *sfont,
                                        int *bank, int *prog);
+fluid_real_t fluid_channel_get_key_pitch(fluid_channel_t *chan, int key);
 
 #define fluid_channel_get_preset(chan)          ((chan)->preset)
 #define fluid_channel_set_cc(chan, num, val) \

src/synth/fluid_voice.c

@@ -670,6 +670,7 @@ calculate_hold_decay_buffers(fluid_voice_t *voice, int gen_base,
      * GEN_KEYTOVOLENVDECAY, GEN_KEYTOMODENVHOLD, GEN_KEYTOMODENVDECAY
      */
 
+    fluid_real_t keysteps;
     fluid_real_t timecents;
     fluid_real_t seconds;
     int buffers;
@@ -681,7 +682,9 @@ calculate_hold_decay_buffers(fluid_voice_t *voice, int gen_base,
      * will cause (60-72)*100=-1200 timecents of time variation.
      * The time is cut in half.
      */
-    timecents = (fluid_voice_gen_value(voice, gen_base) + fluid_voice_gen_value(voice, gen_key2base) * (fluid_real_t)(60 - fluid_voice_get_actual_key(voice)));
+
+    keysteps = 60.0f - fluid_channel_get_key_pitch(voice->channel, fluid_voice_get_actual_key(voice)) / 100.0f;
+    timecents = fluid_voice_gen_value(voice, gen_base) + fluid_voice_gen_value(voice, gen_key2base) * keysteps;
 
     /* Range checking */
     if(is_decay)