diff --git a/doc/7-systems/ga20.md b/doc/7-systems/ga20.md
index b37488e30..57e96efa3 100644
--- a/doc/7-systems/ga20.md
+++ b/doc/7-systems/ga20.md
@@ -4,6 +4,8 @@ it is a 4 channel PCM sound source used by Irem in their arcades in late 1980s a
 
 the sound chip itself is rather unremarkable, having 8-bit volume and pitch control and no stereo panning...
 
+let's be honest. Furnace has too many chips and a great portion of them are sample chips that do the same task: playing back samples.
+
 ## effects
 
 this chip has no added effects.
diff --git a/doc/7-systems/logisticmap.png b/doc/7-systems/logisticmap.png
index ff1d7976d..6737e8c1a 100644
Binary files a/doc/7-systems/logisticmap.png and b/doc/7-systems/logisticmap.png differ
diff --git a/doc/7-systems/ym2612.md b/doc/7-systems/ym2612.md
index 0d584b231..f04cc8b51 100644
--- a/doc/7-systems/ym2612.md
+++ b/doc/7-systems/ym2612.md
@@ -82,6 +82,8 @@ Furnace also offers DualPCM, a Z80 driver that splits channel 6 into two individ
 
 this chip uses the [FM (OPN)](../4-instrument/fm-opn.md) and [Generic Sample](../4-instrument/sample.md) instrument editors.
 
+the maximum PCM playback rate is 26633 Hz.
+
 ## extended channel 3
 
 in ExtCh mode, channel 3 is split into one column for each of its four operators. feedback and LFO levels are shared. the frequency of each operator may be controlled independently with notes and effects. this can be used for more polyphony or more complex sounds.