5.2.6 Interpolation of the ISPs

26.1903GPPAdaptive Multi-Rate - Wideband (AMR-WB) speech codecSpeech codec speech processing functionsTranscoding functionsTS

The set of quantized (and unquantized) LP parameters is used for the fourth subframe whereas the first, second, and third subframes use a linear interpolation of the parameters in the adjacent frames. The interpolation is performed on the ISPs in the domain. Let be the ISP vector at the 4th subframe of the frame, and the ISP vector at the 4th subframe of the past frame n-1. The interpolated ISP vectors at the 1st, 2nd, and 3rd subframes are given by

The same formula is used for interpolation of the unquantized ISPs. The interpolated ISP vectors are used to compute a different LP filter at each subframe (both quantized and unquantized) using the ISP to LP conversion method described in Section 5.2.4.