LSPToLSF

Converts LSP coefficients to LSF coefficients.

Syntax

IppStatus ippsLSPToLSF_Norm_G729_16s (const Ipp16s* pLSP, Ipp16s* pLSF);

IppStatus ippsLSPToLSF_G729_16s (const Ipp16s* pLSP, Ipp16s* pLSF);

Parameters

pLSP	Pointer to the LSP vector, in Q15 in the range [-1:1].
pLSF	Pointer to the LSF vector. Values must be scaled by 13 bits in the range [0:π] (for ippsLSPToLSF_G729_16s function) or by 15 bits in the range [0: 0.5] (for ippsLSPToLSF_Norm_G729_16s function).

Description

These functions are declared in the ippsc.h file. The function ippsLSPToLSF_Norm_G729 converts the LSP coefficients to LSF coefficients as follows:

pLSF[i] = 2^scaleFactor * arccos(pLSP[i]), 0 ≤ i < 10 .

The scale factor is chosen such that the first LSF coefficient is normalized to the interval [0:0.5] by multiplying to 1/π. The function ippsLSPToLSF_G729 retains the result within the interval [0:π ]. Both functions use the same approximation table to calculate the inverse cosine.

Return Values

ippStsNoErr	Indicates no error.
ippStsNullPtrErr	Indicates an error when the pLSP or pLSF pointer is NULL.