ref: eb5aa094c479bc26f3ff88c8e0f262b977a0652e
parent: 9ac1673cd4d6a503cb1a76f63392b6999c3dea22
author: Jean-Marc Valin <[email protected]>
date: Wed Jun 10 13:48:39 EDT 2009
ietf doc: synthesis
--- a/doc/ietf/draft-valin-celt-codec.xml
+++ b/doc/ietf/draft-valin-celt-codec.xml
@@ -376,6 +376,9 @@
<t>X = P + g_f * y,</t>
<t>where g_f = ( sqrt( (y^T*P)^2 + ||y||^2*(1-||P||^2) ) - y^T*P ) / ||y||^2. </t>
+<t>This is described in mix_pitch_and_residual() (<xref target="vq.c">vq.c</xref>).</t>
+
+
<t>
The search for the best codevector y is performed by alg_quant()
(<xref target="vq.c">vq.c</xref>). There are several possible approaches to the
@@ -399,7 +402,13 @@
</section>
-<section anchor="Short windows" title="Short windows">
+<section anchor="synthesis" title="Synthesis">
+<t>
+After all the quantisation is completed, the quantised energy is used along with the
+quantised normalised band data to resynthesise the MDCT spectrum. The inverse MDCT (<xref target="inverse-mdct"></xref>) and the weighted overlap-add are applied and the signal is stored in the <spanx style="emph">synthesis buffer</spanx> so it can be used for pitch prediction.
+The encoder MAY omit this step of the processing if it knows that it will not be using
+the pitch predictor for the next few frames.
+</t>
</section>
@@ -455,7 +464,7 @@
</t>
</section>
-<section anchor="Inverse MDCT" title="Inverse MDCT">
+<section anchor="inverse-mdct" title="Inverse MDCT">
<t>The inverse MDCT implementation has no special characteristic. The
input is N frequency-domain samples and the output is 2*N time-domain
samples. The output is windowed using the same <spanx style="emph">low-overlap</spanx> window