LSPToLPC_GSMAMR

Converts LSPs to LP coefficients.

Syntax

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

Parameters

pSrcLsp	Pointer to the LSP coefficient vector with ten elements, represented using Q0.15.
pDstLpc	Pointer to the LP coefficient vector with 11 elements, 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.