Commit 224824b0 authored by Jean-Marc Valin's avatar Jean-Marc Valin
Browse files

ietf doc: pitch description

parent 66a57c8e
......@@ -443,9 +443,16 @@ transmission of any allocation information.
<section anchor="pitch-prediction" title="Pitch Prediction">
The pitch period is computed by find_spectral_pitch()
(<xref target="pitch.c">pitch.c</xref>) and the pitch gain is computed by
compute_pitch_gain() (<xref target="bands.c">bands.c</xref>).
The pitch period T is computed in the frequency domain using a generalized
cross-correlation, as implemented in find_spectral_pitch()
(<xref target="pitch.c">pitch.c</xref>). An MDCT is then computed on the
synthsis signal memory using the offset T. If there is sufficient energy in this
part of the signal, the pitch gain for each pitch band
is computed as g = X^T*P, where X is the normalised (unquantised) signal and
P is the normalised pitch signal.
The gain is computed by compute_pitch_gain() (<xref target="bands.c">bands.c</xref>)
and if a sufficient number of bands have a high enough gain, then the pitch bit is set.
Otherwise, no use of pitch is made.
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