ref: 945c0c7fa93b4241e44d8d92046c9ffb7cffd240
parent: 8ff61171250502a6059995c05902caf06ab07acf
author: Jean-Marc Valin <[email protected]>
date: Fri Jul 8 07:15:01 EDT 2011
Anti-collapse description
--- a/doc/draft-ietf-codec-opus.xml
+++ b/doc/draft-ietf-codec-opus.xml
@@ -3036,7 +3036,13 @@
<section anchor="anti-collapse" title="Anti-collapse processing">
<t>
-When the frame has the transient bit set...
+When the frame has the transient bit set, an anti-collapse bit is decoded.
+When anti-collapse is set, then the energy in each small MDCT is prevented
+from collapsing to zero. For each band of each MDCT where a collapse is
+detected, a pseudo-random signal is inserted with an energy corresponding
+to the min energy over the two previous frames. A renormalization step is
+then required to ensure that the anti-collapse step did not alter the
+energy preservation property.
</t>
</section>