diff --git a/mixer.py b/mixer.py
index 7ed3639..a5d7448 100755
--- a/mixer.py
+++ b/mixer.py
@@ -6,6 +6,9 @@ import mido
 
 from enum import Enum
 
+# For Allen & Heath Qu MIDI protocol documentation see:
+# https://www.allen-heath.com/content/uploads/2023/06/Qu_MIDI_Protocol_V1.9.pdf
+
 
 class Mixer:
     def __init__(self, ip):