6 Functional description of the decoder

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

The function of the decoder consists of decoding the transmitted parameters (LP parameters, ACELP/TCX mode, adaptive codebook vector, adaptive codebook gain, fixed codebook vector, fixed codebook gain, TCX parameters, high-band parameters, stereo information) and performing synthesis to obtain the reconstructed low-frequency and high-frequency signals. For stereo signal synthesis, the stereo low- and mid-band signals are reconstructed using the low-frequency mono signal and the transmitted and decoded stereo parameters (…).

Section 6.1 describes the reconstruction, by the decoder, of the mono low-band signal in the 0-Fs/4 kHz bandwidth (core ACELP/TCX decoder). The reconstruction of the higher frequency band using bandwidth extension and the mixing of the low and high frequencies of the mono signal will be described respectively in Sections 6.2 and 6.3. The generation of the stereo signals will be described in Section 6.4. Finally, Section 6.5 describes the concealment algorithm in the case of missing frames.