Fine tuning field research.

Subversion-branch: /research
Subversion-revision: 1663

opl/finetune/README

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+Investigations into how the fine tuning field affects OPL register writes.
+
+Findings:
+
+ * Fine tuning only affects double voice instruments.  It is only applied to
+   the second voice and not the first.
+
+ * The fine tuning value adjusts the index into Doom's frequency table.  The
+   offset is divided by two before being applied, so a fine tuning value of
+   10 causes an offset of 5.
+
+ * Due to integer rounding, odd numbered negative offsets are rounded down
+   (away from zero), so a tuning of -3 gives an offset of -2.
+

opl/finetune/gen-sequence

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+#!/usr/bin/env ruby
+
+def note_on(delay, channel, note, volume)
+    # note on
+    putc delay * 6
+    putc 0x90 + channel
+    putc note
+    putc volume
+end
+
+def note_off(delay, channel, note)
+    # note on
+    putc delay * 6
+    putc 0x80 + channel
+    putc note
+    putc 0x00
+end
+
+def program_change(delay, channel, instrument)
+    putc delay * 6
+    putc 0xc0 + channel
+    putc instrument
+end
+
+def end_of_track
+
+    putc 0x00
+    putc 0xff
+    putc 0x2f
+    putc 0x00
+
+end
+
+# Instrument 17 has normal tuning, instrument 18 is +10
+
+program_change(0x1, 1, 17)
+program_change(0x1, 2, 18)
+
+# Play through some notes, making the same note on each of the two channels.
+
+for i in 10..64
+    note_on(10, 1, i, 100)
+    note_on(10, 2, i, 100)
+    note_off(10, 1, i)
+    note_off(0, 2, i)
+end
+
+# end of track
+
+end_of_track
+

opl/finetune/gen-sequence2

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+#!/usr/bin/env ruby
+
+def note_on(delay, channel, note, volume)
+    # note on
+    putc delay * 6
+    putc 0x90 + channel
+    putc note
+    putc volume
+end
+
+def note_off(delay, channel, note)
+    # note on
+    putc delay * 6
+    putc 0x80 + channel
+    putc note
+    putc 0x00
+end
+
+def program_change(delay, channel, instrument)
+    putc delay * 6
+    putc 0xc0 + channel
+    putc instrument
+end
+
+def end_of_track
+
+    putc 0x00
+    putc 0xff
+    putc 0x2f
+    putc 0x00
+
+end
+
+# Instrument 20 has normal tuning, instrument 21 is -3
+
+program_change(0x1, 1, 20)
+program_change(0x1, 2, 21)
+
+# Play through some notes, making the same note on each of the two channels.
+
+for i in 10..64
+    note_on(10, 1, i, 100)
+    note_on(10, 2, i, 100)
+    note_off(10, 1, i)
+    note_off(0, 2, i)
+end
+
+# end of track
+
+end_of_track
+

opl/finetune/results.txt

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+note	chan 1	chan 2			index 1	index 2
+
+10	0x266	0x266, 0x26c		32*10	32*10, 32*10+5
+11	0x28b	0x28b, 0x290		32*11	32*11, 32*11+5
+12	0x158	0x158, 0x2b7		32*0	32*0, 32*12+5
+13	0x16d	0x16d, 0x2e1		32*1	32*1, 32*13+5
+14	0x183	0x183, 0x30d		32*2	32*2, 32*14+5
+15	0x19a	0x19a, 0x33b		32*3	32*3, 32*15+5
+16	0x1b2	0x1b2, 0x36c		32*4	32*4, 32*16+5
+17	0x1cc	0x1cc, 0x3a1		32*5	32*5, 32*17+5
+18	0x1e7	0x1e7, 0x3d8		32*6	32*6, 32*18+5
+19	0x204	0x204, 1/0x209		32*7	32*7, 32*19+5
+20	0x223	0x223, 1/0x228		32*8	32*8, 32*20+5
+21	0x244	0x244, 1/0x249		32*9	32*9, 32*21+5
+22	0x266	0x266, 1/0x26c		32*10	32*10, 32*22+5
+23	0x28b	0x28b, 1/0x290		32*11	32*11, 32*23+5
+24	0x2b1	0x2b1, 1/0x2b7		32*12	32*12, 32*24+5
+25	0x2da	0x2da, 1/0x2e1		32*13	32*13, 32*25+5
+26	0x306	0x306, 1/0x30d		32*14	32*14, 32*26+5
+

opl/finetune/results2.txt

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+note	chan 1	chan 2			index 1	index 2
+
+10	0x266	0x266, 0x264		32*10	32*10, 32*10-2
+11	0x28b	0x28b, 0x288		32*11	32*11, 32*11-2
+12	0x2b1	0x2b1, 0x2af		32*0	32*0, 32*12-2
+13	0x2da	0x2da, 0x2d8		32*1	32*1, 32*13-2
+14	0x306	0x306, 0x303		32*2	32*2, 32*14-2
+15	0x334	0x334, 0x331		32*3	32*3, 32*15-2
+16	0x365	0x365, 0x361		32*4	32*4, 32*16-2
+17	0x398	0x398, 0x395		32*5	32*5, 32*17-2
+18	0x3cf	0x3cf, 0x3cb		32*6	32*6, 32*18-2
+19	0x204	0x204, 1/0x202		32*7	32*7, 32*19-2
+20	0x223	0x223, 1/0x221		32*8	32*8, 32*20-2
+21	0x244	0x244, 1/0x241		32*9	32*9, 32*21-2
+22	0x266	0x266, 1/0x264		32*10	32*10, 32*22-2
+23	0x28b	0x28b, 1/0x288		32*11	32*11, 32*23-2
+24	0x2b1	0x2b1, 1/0x2af		32*12	32*12, 32*24-2
+25	0x2da	0x2da, 1/0x2d8		32*13	32*13, 32*25-2
+26	0x306	0x306, 1/0x303		32*14	32*14, 32*26-2
+