LSPToLPC_GSMAMR

Converts LSPs to LP coefficients.

Syntax

IppStatus ippsLSPToLPC_GSMAMR_16s(const Ipp16s* pSrcLsp, Ipp16s* pDstLpc);

Parameters

pSrcLsp	Pointer to the ten-element LSP coefficient vector, represented using Q0.15.
pDstLpc	Pointer to the eleven-element LP coefficient vector, represented using Q3.12.

Description

The function ippsLSPToLPC_GSMAMR is declared in ippsc.h file. This function converts a set of 10th-order LSPs to LP coefficients. The functionality is as follows:

Calculate the polynomial coefficients of F₁(z) and F₂(z), using the recursive relations

for i = 1 .. 5

f₁(i) = 2q_2i-1* f₁(i-1) + 2f₁(i-2)

for j = i-1 .. 1

f₁(j) = f₁(j) - 2q_2i-1* f₁(j-1) + 2f₁(j-2)

where initial values f₁(0) = 1 and f₁ (-1) = 0. The coefficients f₂(i) are computed similarly by replacing q_2i-1 by q_2i.

2. MultiplyF₁(z) and F₂(z) by 1+z^-1 and 1-z^-1 , respectively, to obtain F'₁(z) and F'₂(z), using the following relations:

f'₁(i) = f₁(i) + f₁(i-1),

f'₂(i) = f₂(i) + f₂(i-1), for i = 1,2, ..., 5.

3. Compute the LP coefficients from the polynomials F'₁(z) and F'₂(z) as follows:

a_i = 0.5f'₁(i) + 0.5f'₂(i) for i = 1,2, ..., 5, and

a_i = 0.5f'₁(11 - i) + 0.5f'₂(11 - i) for i = 6,7, ..., 11.

Return Values

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