6.3.1 Stereo signal low-band synthesis

26.2903GPPAudio codec processing functionsExtended Adaptive Multi-Rate - Wideband (AMR-WB+) codecRelease 17Transcoding functionsTS

The AVQ parameters are decoded in a similar way as described in section 6.1.2, after decoding the step of spectrum de-shaping is performed in order to de-emphasize the spectral coefficients.

The global gain decoding is performed according to Section 6.1. by inverting the 7-bit logarithmic quantization calculated in the encoder as in Section 5.5.1. The signal after inverse transform is multiplied by the global gain in order to produce a time domain signal .

Decoding the balance factor is done by inverting the 7 bit scalar quantizer. In the case of mode 0, a signal envelope is estimated from the mono signal and this signal is compensated for the envelope. The resulting signal is multiplied by the balance factor and added to the time domain signal . The estimated time domain envelope is used in order to shape the resulting signal and reduce the pre-echo artefact when mode 0 is selected in the encoder.

Adaptive overlap-add is used in order to synthesise the time domain side signal which is used to produce the low frequencies left and right signal , .