Add most recent novoices findings.

Subversion-branch: /research
Subversion-revision: 1666

opl/novoices/README

@@ -1,3 +1,25 @@
 Investigating how Doom decides on a voice to discard when it runs out
 of OPL voices.
 
+Findings so far:
+
+ * The instrument affects the voice that is released (different instruments
+   give different results).  It is the instrument data that is significant,
+   not the instrument number (identical instruments behave the same - 87/88)
+ * Sometimes notes are not turned off when they should be.  Sometimes notes
+   are turned off when they should not be (bug?)
+ * DMX maintains a linked list of the most recently-allocated voices.  These
+   are searched backwards when finding a voice to free, so the most recently
+   allocated voices are the first to be freed.
+ * Different MIDI channels have different "priorities", somehow affected
+   by the instrument in use on that channel.
+ * When no voices are available, the will search back through the allocated
+   voices list and discard the most recently used voice from a channel of
+   a lower priority to the channel for the new note.
+ * If no lower-priority voices are available, a voice from the same
+   channel will be discarded.
+ * If no voices from lower priority channels are available, and none from
+   the same channel, the first voice in the list is discarded, ignoring
+   priority.
+ * The "total level" field for the instrument does NOT determine priority.
+

opl/novoices/gen-sequence5

@@ -0,0 +1,91 @@
+#!/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
+
+program_change(0x1, 8, 9)
+program_change(0x1, 1, 7)
+program_change(0x1, 2, 7)
+
+# Turn on some notes and then turn them off, to boost us
+# up to the middle of the range of operators.
+
+note_on(0xf, 8, 0x20, 0x40)        # voice 1
+note_off(0xf, 8, 0x20)
+note_on(0xf, 8, 0x21, 0x40)        # voice 2
+note_off(0xf, 8, 0x21)
+note_on(0xf, 8, 0x22, 0x40)        # voice 3
+note_off(0xf, 8, 0x22)
+
+# Play some notes until we use up all the OPL operators.
+
+note_on(0xf, 8, 0x20, 0x40)                                    # voice 4
+		note_on(0xf, 1, 0x21, 0x40)                    # voice 5
+				note_on(0xf, 2, 0x22, 0x40)    # voice 6
+note_on(0xf, 8, 0x23, 0x40)                                    # voice 7
+		note_on(0xf, 1, 0x24, 0x40)                    # voice 8
+				note_on(0xf, 2, 0x25, 0x40)    # voice 1
+note_on(0xf, 8, 0x26, 0x40)                                    # voice 2
+		note_on(0xf, 1, 0x27, 0x40)                    # voice 3 3-2-1-8-7-6-5-4
+
+# Now all voices are in use ...
+# "no alt" = no inferior channels, first voice from same channel used
+
+note_on(0xf, 8, 0x28, 0x40)                                    # gets v2 2-3-1-8-7-6-5-4 chan 8 < chan 1 (no alt)
+		note_on(0xf, 1, 0x29, 0x40)                    # gets v2                 chan 1 > chan 8
+				note_on(0xf, 2, 0x2a, 0x40)    # gets v7 7-2-3-1-8-6-5-4 chan 8 < chan 1+2
+note_on(0xf, 8, 0x2b, 0x40)                                    # gets v4 4-7-2-3-1-8-6-5 chan 8 < chan 1+2 (no alt)
+		note_on(0xf, 1, 0x2c, 0x40)                    # gets v4                 chan 1 > chan 8
+				note_on(0xf, 2, 0x2d, 0x40)    # gets v7 7-4-2-3-1-8-6-5 chan 2 < chan 1 (no alt)
+note_on(0xf, 8, 0x2e, 0x40)                                    # gets v7                 chan 8 > chan 2? (no alt?)
+		note_on(0xf, 1, 0x2f, 0x40)                    # gets v7                 chan 1 > chan 8
+				note_on(0xf, 2, 0x30, 0x40)    # gets v1 1-7-4-2-3-8-6-5 chan 2 < chan 1 (no alt)
+note_on(0xf, 8, 0x31, 0x40)                                    # gets v1                 chan 8 > chan 2? (no alt?)
+
+# voices off: 5, 7, 1, 3, 2, 8, 6, 4, 0
+
+note_off(0xf, 8, 0x20)
+				note_off(0xf, 1, 0x21)
+note_off(0xf, 8, 0x22)
+				note_off(0xf, 1, 0x23)
+note_off(0xf, 8, 0x24)
+				note_off(0xf, 1, 0x25)
+note_off(0xf, 8, 0x26)
+				note_off(0xf, 1, 0x27)
+note_off(0xf, 8, 0x28)
+				note_off(0xf, 1, 0x29)
+note_off(0xf, 8, 0x2a)
+				note_off(0xf, 1, 0x2b)
+note_off(0xf, 8, 0x2c)
+				note_off(0xf, 1, 0x2d)
+note_off(0xf, 8, 0x2e)
+				note_off(0xf, 1, 0x2f)
+note_off(0xf, 8, 0x30)
+				note_off(0xf, 1, 0x31)
+
+# end of track
+
+putc 0x00
+putc 0xff
+putc 0x2f
+putc 0x00
+