Apply suggestions from code review

Co-authored-by: Paul Adenot <paul@paul.cx>

Author: Hernqvist

index.bs

@@ -11586,8 +11586,9 @@ Underruns are defined in terms of [=underrun frames=] and [=underrun events=]:
 - An <dfn>underrun frame</dfn> is an audio frame played by the output device
     that was not provided by the AudioContext.
     This happens when the playout path fails to provide audio frames
-    to the output device on time, in which case underrun frames will be played
-    (underrun frames are typically silence).
+    to the output device on time, in which case it will still have to play something.
+    
+    NOTE: Underrun frames are typically silence.
     This typically only happens if the pipeline is underperforming.
     This includes underrun situations that happen for reasons unrelated to
     WebAudio/{{AudioWorklet}}s.