update readme

README.md

@@ -2,14 +2,18 @@
 
 ![screenshot](papers/screenshot.png)
 
-this is a work-in-progress editor for DefleMask module files (.dmf).
+this is a work-in-progress chiptune tracker compatible with DefleMask modules (.dmf).
 
 ## features
 
 - supports Sega Genesis, Master System, Game Boy, PC Engine, NES, C64, YM2151/PCM and Neo Geo!
+- multiple sound chips in a single song!
 - clean-room design (zero reverse-engineered code and zero decompilation; using official DMF specs, guesswork and ABX tests only)
 - bug/quirk implementation for increased playback accuracy
 - accurate emulation cores whether possible (Nuked, MAME, SameBoy, Mednafen PCE, puNES, reSID and ymfm)
+- additional features on top;
+  - SSG envelopes in Neo Geo
+  - full duty/cutoff range in C64
 - open-source. GPLv2.
 
 ## downloads
@@ -81,6 +85,28 @@ this will render a .dmf file to .wav.
 
 # notes
 
+> how do I use Neo Geo SSG envelopes?
+
+the following effects are provided:
+
+- `22xy`: set envelope mode.
+  - `x` sets the envelope shape, which may be one of the following:
+    - `0: \___` decay
+    - `4: /___` attack once
+    - `8: \\\\` saw
+    - `9: \___` decay
+    - `A: \/\/` inverse obelisco
+    - `B: \¯¯¯` decay once
+    - `C: ////` inverse saw
+    - `D: /¯¯¯` attack
+    - `E: /\/\` obelisco
+    - `F: /___` attack once
+  - if `y` is 1 then the envelope will affect this channel.
+- `23xx`: set envelope period low byte.
+- `24xx`: set envelope period high byte.
+
+a lower envelope period will make the envelope run faster.
+
 > my song sounds very odd at a certain point
 
 file a bug report. use the Issues page.
@@ -90,3 +116,7 @@ it's probably another playback inaccuracy.
 > my song sounds correct, but it doesn't in DefleMask
 
 file a bug report **here**. it still is a playback inaccuracy.
+
+> my C64 song sounds terrible after saving as .dmf!
+
+that's a limitation of the DefleMask format. save in Furnace song format instead (.fur).