diff --git a/src/engine/platform/ay.cpp b/src/engine/platform/ay.cpp
index 6f50214cc..2bfc36fff 100644
--- a/src/engine/platform/ay.cpp
+++ b/src/engine/platform/ay.cpp
@@ -266,6 +266,8 @@ void DivPlatformAY8910::tick(bool sysTick) {
     }
     if (chan[i].std.wave.had) {
       if (!(chan[i].nextPSGMode.val&8)) {
+        // TODO: clean up.
+        // why does Defle start from 1?!
         chan[i].nextPSGMode.val=(chan[i].std.wave.val+1)&7;
         if (chan[i].active) {
           chan[i].curPSGMode.val=chan[i].nextPSGMode.val;
diff --git a/src/engine/platform/ay8930.cpp b/src/engine/platform/ay8930.cpp
index 6fca42e06..c32e57987 100644
--- a/src/engine/platform/ay8930.cpp
+++ b/src/engine/platform/ay8930.cpp
@@ -256,6 +256,8 @@ void DivPlatformAY8930::tick(bool sysTick) {
     }
     if (chan[i].std.wave.had) {
       if (!(chan[i].nextPSGMode.val&8)) {
+        // TODO: clean up.
+        // why does Defle start from 1?!
         chan[i].nextPSGMode.val=(chan[i].std.wave.val+1)&7;
         if (chan[i].active) {
           chan[i].curPSGMode.val=chan[i].nextPSGMode.val;