5.2.6 Interpolation of the LSPs

26.0903GPPAdaptive Multi-Rate (AMR) speech codecMandatory speech CODEC speech processing functionsRelease 17Transcoding functionsTS

12.2 kbit/s mode

The two sets of quantified (and unquantized) LP parameters are used for the second and fourth subframes whereas the first and third subframes use a linear interpolation of the parameters in the adjacent subframes. The interpolation is performed on the LSPs in the domain. Let be the LSP vector at the 4^th subframe of the present frame , be the LSP vector at the 2^nd subframe of the present frame , and the LSP vector at the 4^th subframe of the past frame . The interpolated LSP vectors at the 1^st and 3^rd subframes are given by:

(27)

The interpolated LSP vectors are used to compute a different LP filter at each subframe (both quantified and unquantized coefficients) using the LSP to LP conversion method described in clause 5.2.4.

10.2, 7.95, 7.40, 6.70, 5.90, 5.15, 4.75 kbit/s modes

The set of quantified (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 subframes. The interpolation is performed on the LSPs in the domain. The interpolated LSP vectors at the 1^st, 2^nd, and 3^rd subframes are given by:

(28)

The interpolated LSP vectors are used to compute a different LP filter at each subframe (both quantified and unquantized coefficients) using the LSP to LP conversion method described in clause 5.2.4.