ref: 4570db6af307d016d789124ad8b1990f07a8b6c7
parent: 4c0e25fcdd0c156c4076a8e699b532ba7479b673
author: Jean-Marc Valin <[email protected]>
date: Wed Sep 7 13:15:34 EDT 2011
Oops, remove duplicate description of the MDCT
--- a/doc/draft-ietf-codec-opus.xml
+++ b/doc/draft-ietf-codec-opus.xml
@@ -4368,21 +4368,6 @@
<section anchor="inverse-mdct" title="Inverse MDCT">
-<t>The MDCT implementation has no special characteristics. The
-input is a windowed signal (after pre-emphasis) of 2*N samples and the output is N
-frequency-domain samples. A "low-overlap" window is used to reduce the algorithmic delay.
-It is derived from a basic (full overlap) window that is the same as the one used in the Vorbis codec:
-<figure align="center">
-<artwork align="center"><![CDATA[
- pi pi n + 1/2 2
-W(n) = [sin(-- * sin(-- * -------))] .
- 2 2 L
-]]></artwork>
-</figure>
-The low-overlap window is created by zero-padding the basic window and inserting ones in the middle, such that the resulting window still satisfies power complementarity. The MDCT is computed in mdct_forward() (mdct.c), which includes the windowing operation and a scaling of 2/N.
-</t>
-
-
<t>The inverse MDCT implementation has no special characteristics. The
input is N frequency-domain samples and the output is 2*N time-domain
samples, while scaling by 1/2. A "low-overlap" window is used to reduce the algorithmic delay.
@@ -4389,9 +4374,10 @@
It is derived from a basic (full overlap) 240-sample version of the window used by the Vorbis codec:
<figure align="center">
<artwork align="center"><![CDATA[
- pi pi n + 1/2 2
-W(n) = [sin(-- * sin(-- * -------))] .
- 2 2 L
+ 2
+ / /pi /pi n + 1/2\ \ \
+W(n) = |sin|-- * sin|-- * -------| | | .
+ \ \2 \2 L / / /
]]></artwork>
</figure>
The low-overlap window is created by zero-padding the basic window and inserting ones in the