notes.txt: update notes

doc/notes.txt

@@ -10,9 +10,19 @@ TODO:
 + Select and save audio devices.
 + Mac Conversion
 + Live MIDI - to test audio/MIDI delay.
-
++ As threshold increases overall volume decreases - add a compensation algorithm.
++ THere are unintialized variable warnings on the release build.
 
 BUGS:
+// Apr 20
+The tempo measurement can produce invalid values.  Set score to 22 then play Mark 38.
+First tempo measurement is a non-sense value - probably produced by an div by zero.
+
+Crash on playing Mark 37.
+
+Click on list control outside below list item - crash!
+
+
 
 // Feb 27
 + Audio seems to preceded MIDI by around 250ms this probably arises