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 |
|---|---|
| Basic Functions | |
| 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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