LSFDecode

Performs inverse quantization of LSFs.

Syntax

IppStatus ippsLSFDecode_G723_16s (const Ipp16s* pQuantIndex, const Ipp16s* pPrevLSF, int erase, Ipp16s* pQuantLSF);

Parameters

pQuantIndex	Pointer to the input LSP VQ indices vector [3].
pPrevLSF	Pointer to the input quantized LSF for previous subframes.
erase	Indicates frame erasure.
pQuantLSF	Pointer to the output quantized LSF for previous subframes.

Description

The function ippsLSFDecode_G723 is declared in the ippsc.h file. This function performs inverse quantization of LSFs (in other words, decodes LSP VQ indices). First three VQ table entries corresponding to the transmitted index are found. The predicted vector is added to the found vector and DC vector to form the decoded vectors in three bands separately. A stability check is performed to ensure the difference between them not is less then 31.25 Hz.

For erased frame, zero predicted vectors are chosen and stability check for the difference in 62.5 Hz is applied.

Return Values

ippStsNoErr	Indicates no error.
ippStsNullPtrErr	Indicates an error when one of the specified pointers is NULL.
ippStsLSFLow	Indicates a warning when a stability condition is not met.