6.3.2 Stereo Signal Mid-Band synthesis
26.2903GPPAudio codec processing functionsExtended Adaptive Multi-Rate - Wideband (AMR-WB+) codecRelease 17Transcoding functionsTS
The mono mid-band signal is filtered in order to obtain the mid-band excitation signal 
. The filter and the corresponding gains are decoded by using the inverse operation of the predictive multistage quantizer (MSPVQ-1) and the predictive 2 dimensional vector quantizer (PVQ-1).
The filter is used to filter the excitation signal 
according to
the two channels pseudo-excitations are computed as:
Windowing and overlap add is used in norder to smooth the frame transitions. The anount of overlap is equal to 
according to the following figure
The output of the overlap add sections are finally inverse filtered by the core low band signal lpc filter 
to produce the left and right mid-band signals 
and 
.