MIDI: Increase percision of synthesizer by a factor of 4 - makes certain parts (guitar bends, mostly)

sound more natural. Also, completely rearrange the order of operations in the delta computation. Had to 
use long longs. Probably not a good idea for speed, but the order can be optimized more later.


git-svn-id: svn://svn.rockbox.org/rockbox/trunk@15652 a1c6a512-1295-4272-9138-f99709370657

2 files changed, 19 insertions, 4 deletions

diff --git a/apps/plugins/midi/midiutil.h b/apps/plugins/midi/midiutil.h
index 18d493b23a..c3c5d91f47 100644
--- a/apps/plugins/midi/midiutil.h
+++ b/apps/plugins/midi/midiutil.h
@@ -17,7 +17,7 @@
  *
  ****************************************************************************/
 
-#define FRACTSIZE 10
+#define FRACTSIZE 12
 
 #define BUF_SIZE 8192 /* 32 kB output buffers */
 #define NBUF   2
diff --git a/apps/plugins/midi/sequencer.c b/apps/plugins/midi/sequencer.c
index bd2f33b365..e2a9f7dd5c 100644
--- a/apps/plugins/midi/sequencer.c
+++ b/apps/plugins/midi/sequencer.c
@@ -144,10 +144,25 @@ static void findDelta(struct SynthObject * so, int ch, int note)
 {
     struct GWaveform * wf = patchSet[chPat[ch]]->waveforms[patchSet[chPat[ch]]->noteTable[note]];
     so->wf=wf;
-    unsigned int delta= 0;
+
+    /* Used to be unsigned int, but math had to be done in different order to avoid overflow */
+    unsigned long long delta= 0;
+
+/*
+    Old formula:
     delta = (((gustable[note+chPBNoteOffset[ch]]<<FRACTSIZE) / (wf->rootFreq)) * wf->sampRate / (SAMPLE_RATE));
-    delta = (delta * chPBFractBend[ch])>> 16;
 
+    Plus some pitch stuff. See old SVN for how it used to be
+*/
+
+    delta = (((gustable[note+chPBNoteOffset[ch]]))); /* anywhere from 8000 to 8000000 */
+    delta = delta * wf->sampRate;           /* approx 20000 - 44000 but can vary with tuning */
+    delta = (delta * chPBFractBend[ch]);    /* approx 60000 - 70000 */
+    delta = delta / (SAMPLE_RATE);  /* 44100 or 22050 */
+    delta = delta / (wf->rootFreq); /* anywhere from 8000 to 8000000 */
+
+    /* Pitch bend is encoded as a fractional of 16 bits, hence the 16 */
+    delta = delta >> (16 - FRACTSIZE);  /* a shift of approx 4 bits */
     so->delta = delta;
 }
 
@@ -250,7 +265,7 @@ inline void pressNote(int ch, int note, int vol)
 
             struct GWaveform * wf = drumSet[note]->waveforms[0];
             voices[a].wf=wf;
-            voices[a].delta = (((gustable[note]<<10) / wf->rootFreq) * wf->sampRate / SAMPLE_RATE);
+            voices[a].delta = (((gustable[note]<<FRACTSIZE) / wf->rootFreq) * wf->sampRate / SAMPLE_RATE);
             if(wf->mode & 28)
 //                printf("\nWoah, a drum patch has a loop. Stripping the loop...");
             wf->mode = wf->mode & (255-28);