LSFQuant

Quantizes LSF coefficients.

Syntax

IppStatus ippsLSFQuant_G723_16s32s(const Ipp16s* pSrcLSF, const Ipp16s* pSrcPrevLSF, Ipp32s* pResultQLSFIndex);

Parameters

pSrcLSF	Pointer to the LSF coefficients vector [10], in Q15.
pSrcPrevLSF	Pointer to the previous LSF coefficients vector [10], in Q15.
pResultQLSFIndex	Pointer to the combined index of quantized LSF coefficients. The combination is built by left-shifting the first codebook index by 16 bits and left-shifting the second codebook index by 8 bits, and then adding together the two shifted indices and the third codebook index.

Description

The function ippsLSFQuant_G723 is declared in the ippsc.h file. This function quantizes the LSF coefficients to obtain the codebook indices using PSVQ. It implements the following operations:

1. Calculate the diagonal weighting matrix W, determined from the unquantized LSF coefficients, as:

w_1,1 = 1/ (ω₂-ω₁),

w_10,10 = 1/ (ω₁₀-ω₉),

w_j,j = 1/ min(ω_j-ω_j-1, ω_j+1-ω_j) , j = 2...9

2. Calculate the prediction LSF coefficients as given by:

ω_p = (ω -ω_DC) - 0.375 (ω_-1-ω_DC)

where ω are the current LSF coefficients, ω_-1 are the previous LSF coefficients, and ω_DC are the DC LSF coefficients.

3. Search the codebook vector to minimize the following error:

E_l = (ω_p -ω_l)^TW(ω_p -ω_l) ,

where ω_l is the l-th code vector in the codebook. The quantization uses 3-3-4 split.

Return Values

ippStsNoErr	Indicates no error.
ippStsNullPtrErr	Indicates an error when one of the specified pointers is NULL.