--- a/webaudio/specification.html	Fri Oct 05 15:40:57 2012 -0700
+++ b/webaudio/specification.html	Fri Oct 05 17:35:05 2012 -0700
@@ -3660,7 +3660,7 @@
         output = 0.25 * (input.L + input.R + input.SL + input.SR);
 
     5.1 -> 1 : 5.1 to mono
-        ???
+        output = 0.7071 * (input.L + input.R) + input.C + 0.5 * (input.SL + input.SR)
 
 
 Stereo down-mix:
@@ -3670,7 +3670,16 @@
         output.R = 0.5 * (input.R + input.SR);
 
     5.1 -> 2 : 5.1 to stereo
-        ???</pre>
+        output.L = L + 0.7071 * (input.C + input.SL)
+        output.R = R + 0.7071 * (input.C + input.SR)
+
+    5.1 -&gt; 4 : 5.1 to quad
+        output.L = L + 0.7071 * input.C
+        output.R = R + 0.7071 * input.C
+        output.SL = input.SL
+        output.SR = input.SR
+
+</pre>
 </div>
 
 <div id="Spatialization-section" class="section">