QMF Functions

A Quadrature Mirror Filter (QMF) bank is used by MPEG-4 SBR decoder. QMF consists of:

Analysis Filter Synthesis Filter Synthesis Down Filter.

QMF filterbanks use the functions given below in low power (LP) and high quality (HQ) modes. Each mode is characterized by three function groups:

AnalysisFilter SynthesisFilter SynthesisDownFilter.

To use the SBR_QMF functions, initialize the corresponding filter specification structure, which contains tables of twiddle factors and internal buffer. To allocate memory and initialize the structure, call ipps(**)FilterInitAlloc_SBR_(***) functions, where (**) is a function group name, that is Analysis, Synthesis or SynthesisDown, and (***) is a flavor descriptor (for example, _SBRHQ_32s32sc, _SBRLP_32s). Currently, this method of the specification structure initialization is implemented only for operations on fixed-point signal.

Alternatively, the structure can be initialized by functions for initialization and size getting. In that case, the general operational algorithm is as follows:

The use of the functions described in this section is demonstrated in Intel® IPP Samples downloadable from http://www.intel.com/cd/software/products/asmo-na/eng/220046.htm.


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