6.8.4 CNG decoding

26.4453GPPCodec for Enhanced Voice Services (EVS)Detailed algorithmic descriptionRelease 15TS

The CNG decoding in AMR-WB-interoperable mode is described by referring to subclause 6.7.2. The CNG parameter updates in active and inactive periods is the same as described in subclasue 6.7.2.1.1. The DTX-hangover based parameter analysis is the same as described in subclause 6.7.2.1.2. The quantized logarithmic excitation energy is found from the SID frame using Δ = 2.625 and converted to linear domain using the procedure described in subclause 5.6.2.1.5. The quantized energy is used to obtain the smoothed quantized excitation energy used for CNG synthesis in the same way as described in subclause 5.6.2.1.6. The quantized ISF vector is found in the same way as described in subclause 5.7.12. The smoothed LP synthesis filter, , is then obtained in the same way as described in subclause 5.6.2.1.4 with the only difference that the ISP vector is used instead of the LSP vector. The CNG excitation signal, , where is the frame length, is generated in the same way the random excitation signal is generated as described in subclause 6.7.2.1.5. The comfort noise is synthesized by filtering the excitation signal, , through the smoothed LP synthesis filter, .