diff --git a/doc/4-instrument/ay8910.md b/doc/4-instrument/ay8910.md
index 730faff96..711e8d679 100644
--- a/doc/4-instrument/ay8910.md
+++ b/doc/4-instrument/ay8910.md
@@ -35,3 +35,7 @@ note that timer effects might not be supported by VGM players, and are rather CP
 - **AutoEnv Num**: sets the envelope to the channel's frequency multiplied by numerator.
 - **AutoEnv Den**: sets the envelope to the channel's frequency multiplied by denominator.
   - these two must be set in order for AutoEnv to work!
+- **Force Period**: sets the tone period (wavelength).
+  - overrides Arpeggio and Pitch macros.
+- **Env Period**: sets the envelope period.
+  - ignored if both AutoEnv macros are set.
diff --git a/doc/4-instrument/ay8930.md b/doc/4-instrument/ay8930.md
index 7bec40073..118f15665 100644
--- a/doc/4-instrument/ay8930.md
+++ b/doc/4-instrument/ay8930.md
@@ -29,5 +29,9 @@ note that using samples on AY is CPU expensive!
 - **AutoEnv Num**: sets the envelope to the channel's frequency multiplied by numerator.
 - **AutoEnv Den**: sets the envelope to the channel's frequency multiplied by denominator.
   - these two must be set in order for AutoEnv to work!
+- **Force Period**: sets the tone period (wavelength).
+  - overrides Arpeggio and Pitch macros.
+- **Env Period**: sets the envelope period.
+  - ignored if both AutoEnv macros are set.
 - **Noise AND Mask**: alters the shape/frequency of the noise generator, allowing to produce various interesting sound effects and even PWM phasing.
 - **Noise OR Mask**: see above.