diff --git a/DOCS/sound.html b/DOCS/sound.html
index 3a3ebaca4b..e97e863e67 100644
--- a/DOCS/sound.html
+++ b/DOCS/sound.html
@@ -273,7 +273,8 @@ To use this feature you need a sound card supporting at least 4 channels.</P>
 
 <P>The default coefficient (<CODE>mul</CODE>) is a float number that defaults
   to 2.5. If you set it to 0.0, you will have mono sound (average of both
-  channels). If you set it to 1.0, sound will be unchanged.</P>
+  channels). If you set it to 1.0, sound will be unchanged, if you set it to
+  -1.0, left and right channels will be swapped.</P>
 
 
 <P><B><A NAME=2.3.2.2.7>2.3.2.2.7. Volume normalizer</A></B></P>