diff --git a/doc/4-instrument/ay8910.md b/doc/4-instrument/ay8910.md
index b47e46444..730faff96 100644
--- a/doc/4-instrument/ay8910.md
+++ b/doc/4-instrument/ay8910.md
@@ -1,6 +1,6 @@
 # AY-3-8910 instrument editor
 
-the AY-3-8910 instrument editor consists of two tabs.
+the AY-3-8910 instrument editor consists of three tabs.
 
 ## Sample
 
@@ -10,6 +10,13 @@ the only differences are the lack of an "Use wavetable" option, and the presence
 
 note that using samples on AY is CPU expensive!
 
+## Timer Macros
+- **Timer FX**: timer effect type sequence. 0- off, 1- tone PWM, 2- envelope distortion, 3- reserved
+- **TFX Offset**: PWM speed sequence.
+- **Timer Num and Den**: multiplier of a virtual square wave modulator (?)
+- **PWM Boundary**: sets the range of a pulse width modulation
+
+note that timer effects might not be supported by VGM players, and are rather CPU expensive!
 ## Macros
 
 - **Volume**: volume sequence.