the final part of extra FM effects

papers/doc/7-systems/opll.md

@@ -2,17 +2,17 @@
 
 the YM2413, otherwise known as OPLL, is a cost-reduced FM synthesis sound chip, based on the Yamaha YM3812 (OPL2). thought OPL was downgraded enough? :p
 
-OPLL spawned also a few derivative chips, the best known of these is:
-- the myth. the legend. THE VRC7. 6 channels, *rather interesting* instruments sound bank, no drums mode
+OPLL also spawned a few derivative chips, the best known of these is:
+- the famous Konami VRC7. used in the Japan-only video game Lagrange Point, it was **another** cost reduction on top of the OPLL! this time just 6 channels...
 - Yamaha YM2423, same chip as YM2413, just a different patch set
-- Yamaha YMF281, ditto 
+- Yamaha YMF281, ditto
 
 # technical specifications
 
 the YM2413 is equipped with the following features:
 
 - 9 channels of 2 operator FM synthesis
-- A drum/percussion mode, replacing the last 3 voices with 3 rhythm channels
+- A drum/percussion mode, replacing the last 3 voices with 5 rhythm channels
 - 1 user-definable patch (this patch can be changed throughout the course of the song)
 - 15 pre-defined patches which can all be used at the same time
 - Support for ADSR on both the modulator and the carrier

papers/doc/7-systems/ym2612.md

@@ -39,14 +39,14 @@ one of two chips that powered the Sega Genesis. It is a six-channel, four-operat
 - `53xy` set DT of operator.
   - `x` is the operator (1-4). a value of 0 means "all operators".
   - `y` is the value:
-    - 0: +0
-    - 1: +1
-    - 2: +2
-    - 3: +3
-    - 4: -0
-    - 5: -3
-    - 6: -2
-    - 7: -1
+    - 0: -3
+    - 1: -2
+    - 2: -1
+    - 3: 0
+    - 4: 1
+    - 5: 2
+    - 6: 3
+    - 7: -0
 - `54xy` set RS of operator.
   - `x` is the operator (1-4). a value of 0 means "all operators".
   - `y` is the value.