diff --git a/doc/4-instrument/c64.md b/doc/4-instrument/c64.md
index 8c4ca86a..2f3a9737 100644
--- a/doc/4-instrument/c64.md
+++ b/doc/4-instrument/c64.md
@@ -7,7 +7,7 @@ The C64 instrument editor consists of two tabs: "C64" to control various paramet
 - [Waveform] - allows selecting a waveform. NOTE: more than one waveform can be selected at once, logical AND mix of waves will be produced, with an exception of a noise waveform, it can't be mixed.
 - [Attack] - determines the rising time for the sound. The bigger the value, the slower the attack. (0-15 range)
 - [Decay]- Determines the diminishing time for the sound. The higher the value, the longer the decay. It's the initial amplitude decay rate. (0-15 range)
-- [Sustain] - Determines the diminishing time for the sound. The higher the value, the longer the decay. This is the long "tail" of the sound that continues as long as the key is depressed. (0-15 range)
+- [Sustain] - Sets the volume level at which the sound stops decaying and holds steady. (0-15 range)
 - [Release] - Determines the rate at which the sound disappears after KEY-OFF. The higher the value, the longer the release. (0-15 range)
 - [Ring Modulation] - enables the ring modulation affecting the instrument.
 - [Duty] - specifies the width of a pulse wave. (0-4095 range)
@@ -19,8 +19,8 @@ The C64 instrument editor consists of two tabs: "C64" to control various paramet
 - [Filter mode] - determined the filter mode NOTE: SID's filter is multi-mode, you can mix different modes together (like low and high-pass filters at once) CH3-OFF disables the channel 3, for no reason whatsoever lmao
 - [Volume Macro is Cutoff Macro] - turns a volume macro in a macros tab into a filter cutoff macro.
 - [Absolute Cutoff Macro] - changes the behaviour of a cutoff macro from the old-style, compatible to much more define-able.
-- [Absolute Duty Macro] - changes the behaviour of a duty cycle macro from the old-style, compatible to much more define-able.
-- [Don't test/gate before new note] - (document this)
+- [Absolute Duty Macro] - changes the behaviour of a duty cycle macro from the old-style, compatible to much more definable.
+- [Don't test/gate before new note] - Don't reset the envelope to zero when a new note starts. (Read "Test/Gate" below for more info.)
 
 ## Macros
 
@@ -32,4 +32,4 @@ The C64 instrument editor consists of two tabs: "C64" to control various paramet
 - [Filter mode] - select the filter mode/sequence
 - [Resonance] - filter resonance sequence
 - [Special] - ring and oscillator sync selector
-- [Test/Gate] - (document this)
\ No newline at end of file
+- [Test/Gate] - When on, the TEST bit resets and locks Oscillator 1 at zero until cleared. The GATE bit controls Oscillator 1's envelope: Gate on runs through the envelope's attack, delay, and sustain; Gate off is envelope release.
\ No newline at end of file
diff --git a/doc/4-instrument/n163.md b/doc/4-instrument/n163.md
index 88a7b4ca..4cd12261 100644
--- a/doc/4-instrument/n163.md
+++ b/doc/4-instrument/n163.md
@@ -1,6 +1,6 @@
 # Namco 163 instrument editor
 
-The Namco 163 instrument editor consists of two tabs: "Namco 163" for control of various waveform parameters, and "Macro" containing seveeral macros.
+The Namco 163 instrument editor consists of two tabs: "Namco 163" for control of various waveform parameters, and "Macro" containing several macros.
 
 ## Namco 163