This part of the chapter describes the Intel IPP functions that can be combined to construct a bit-exact implementation of the European Telecommunications Standards Institute (ETSI) Global System for Mobile Communications (GSM) Adaptive Multi-Rate (AMR) ETSI EN 301 704 GSM 06.90 version 7.5.0 Release 2001 speech codec, more commonly known as the GSM-AMR 06.90 codec. The primitives are primarily concerned with the well-defined, computationally expensive core operations that comprise the codec portion of the GSM-AMR system.
The GSM 06.90 AMR speech codec comprises an adaptive multi-rate algorithm that represents efficiently telephone-bandwidth digital speech using compressed data rates of 4.75, 5.15, 5.90, 6.70, 7.40, 7.95, 10.2, and 12.2 kilobits per second (kbps). The GSM-AMR system adaptively controls speech codec bit rates such that output quality is maximized for a given set of channel conditions.
These functions are used in the Intel IPP GSM/AMR Speech Encoder-Decoder sample downloadable from http://www.intel.com/cd/software/products/asmo-na/eng/220046.htm.
The following table provides a list of these functions.
|Function Base Name||Operation|
|Interpolate_GSMAMR||Computes the weighted sum of two vectors.|
|FFTFwd_RToPerm_GSMAMR||Computes the forward fast Fourier transform (FFT) of a real signal.|
|Linear Prediction Analysis Functions|
|AutoCorr_GSMAMR||Estimates the autocorrelation sequence for a block of samples.|
|LevinsonDurbin_GSMAMR||Calculates the LP coefficients using the Levinson-Durbin algorithm.|
|LPCToLSP_GSMAMR||Converts LP coefficients to line spectrum pairs.|
|LSFToLSP_GSMAMR||Converts Line Spectral Frequencies to LSP coefficients.|
|LSPToLPC_GSMAMR||Converts LSPs to LP coefficients.|
|QuantLSPDEcode_GSMAMR||Quantizes the LSP coefficient vector.|
|Adaptive Codebook Search Functions|
|OpenLoopPitchSearchNonDTX_GSMAMR||Computes the OLP lag.|
|OpenLoopPitchSearchDTXVAD1_GSMAMR||Extracts an OLP lag estimate (VAD 1 scheme is enabled).|
|OpenLoopPitchSearchDTXVAD2_GSMAMR||Extracts an OLP lag estimate (VAD 2 scheme is enabled).|
|AdaptiveCodebookSearch_GSMAMR||Performs the adaptive codebook search.|
|AdaptiveCodebookDecode_GSMAMR||Decodes the adaptive codebook parameters.|
|ImpulseResponseTarget_GSMAMR||Computes the impulse response and target signal required for the adaptive codebook search.|
|AdaptiveCodebookGain_GSMAMR||Calculates the gain of the adaptive-codebook vector and the filtered codebook vector.|
|Fixed Codebook Search Functions|
|AlgebraicCodebookSearch_GSMAMR||Searches the algebraic codebook.|
|FixedCodebookDecode_GSMAMR||Decodes the fixed codebook vector.|
|Discontinuous Transmission functions|
|Preemphasize_GSMAMR||Computes pre-emphasis of an input signal in VAD option 2.|
|VAD1_GSMAMR||Implements the VAD functionality corresponding to VAD option 1.|
|VAD2_GSMAMR||Implements the VAD functionality corresponding to VAD option 2.|
|EncDTXSID_GSMAMR||Extracts parameters for the SID frame.|
|EncDTXHandler_GSMAMR||Determines the SID flag of current frame.|
|EncDTXBuffer_GSMAMR, DecDTXBuffer_GSMAMR||Buffer the LSP (or LSF) coefficients and previous log energy coefficients.|
|Post Processing Functions|
|PostFilter_GSMAMR||Filters the synthesized speech.|
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