diff --git a/doc/7-systems/opl.md b/doc/7-systems/opl.md
index 2937fa8935..d0699f07d3 100644
--- a/doc/7-systems/opl.md
+++ b/doc/7-systems/opl.md
@@ -82,3 +82,5 @@ afterwards everyone moved to Windows and software mixed PCM streaming...
 ## info
 
 this chip uses the [FM (OPL)](../4-instrument/fm-opl.md) instrument editor.
+
+when two channels are joined for 4-op mode, the channel bar will show `4OP` on a bracket tying them together.
\ No newline at end of file
diff --git a/doc/7-systems/pokey.md b/doc/7-systems/pokey.md
index eff37cd8c1..ca7d21b1d8 100644
--- a/doc/7-systems/pokey.md
+++ b/doc/7-systems/pokey.md
@@ -39,3 +39,7 @@ a sound and input chip developed by Atari for their 8-bit computers (Atari 400,
 ## info
 
 this chip uses the [POKEY](../4-instrument/pokey.md) instrument editor.
+
+when two channels are joined for filtered output, the channel bar will show `filter` on a bracket tying them together.
+
+when two channels are joined for wide period range, the channel bar will show `16-bit` on a bracket tying them together.
diff --git a/doc/7-systems/snes.md b/doc/7-systems/snes.md
index d10b20c395..76da944ff3 100644
--- a/doc/7-systems/snes.md
+++ b/doc/7-systems/snes.md
@@ -65,6 +65,8 @@ Furnace also allows the SNES to use wavetables (and the wavetable synthesizer) i
 
 this chip uses the [SNES](../4-instrument/snes.md) instrument editor.
 
+when two channels are joined for pitch modulation, the channel bar will show `mod` on a bracket tying them together.
+
 ## channel status
 
 the following icons are displayed when channel status is enabled in the pattern view: