diff --git a/services/audioflinger/Threads.h b/services/audioflinger/Threads.h
index fa047fa..ae8bbb9 100644
--- a/services/audioflinger/Threads.h
+++ b/services/audioflinger/Threads.h
@@ -927,6 +927,8 @@
                                }
                            }
                 // the FastMixer performs mono blend if it exists.
+                // Blending with limiter is not idempotent,
+                // and blending without limiter is idempotent but inefficient to do twice.
     virtual     bool       requireMonoBlend() { return mMasterMono.load() && !hasFastMixer(); }
 };