LSF split vector quantization for wideband codecs with narrowband tandemming

We present the results of a series of experiments to identify the optimum bit allocation for split LSF VQ for both wideband and narrowband mixed speech. This situation arises for both the GSM AMR wideband and the ITU-T wideband standardisation efforts where tandemming with narrowband codecs will occur. We have chosen to study 40 bit 18th-order LSF VQ calculated on 20 ms frames with different degrees of moving average (MA) prediction in order to exploit the interframe correlation gains available whilst minimising error propagation.