diff --git a/src/engine/platform/gb.cpp b/src/engine/platform/gb.cpp
index ea6ad7719..d25cc2118 100644
--- a/src/engine/platform/gb.cpp
+++ b/src/engine/platform/gb.cpp
@@ -289,6 +289,7 @@ int DivPlatformGB::dispatch(DivCommand c) {
         chan[c.chan].ins=c.value;
         if (c.chan!=2) {
           chan[c.chan].vol=parent->getIns(chan[c.chan].ins)->gb.envVol;
+          // TODO: also change envelope values
         }
       }
       break;
diff --git a/src/engine/playback.cpp b/src/engine/playback.cpp
index aea9e1f8b..8042e2cde 100644
--- a/src/engine/playback.cpp
+++ b/src/engine/playback.cpp
@@ -905,8 +905,16 @@ void DivEngine::processRow(int i, bool afterDelay) {
         break;
       case 0x07: // tremolo
         // TODO
+        // this effect is really weird. i thought it would alter the tremolo depth but turns out it's completely different
+        // this is how it works:
+        // - 07xy enables tremolo
+        // - when enabled, a "low" boundary is calculated based on the current volume
+        // - then a volume slide down starts to the low boundary, and then when this is reached a volume slide up begins
+        // - this process repeats until 0700 or 0Axy are found
+        // - note that a volume value does not stop tremolo - instead it glitches this whole thing up
         break;
       case 0x0a: // volume ramp
+        // TODO: non-0x-or-x0 value should be treated as 00
         if (effectVal!=0) {
           if ((effectVal&15)!=0) {
             chan[i].volSpeed=-(effectVal&15)*64;