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. |

- Basic Functions

- LP Analysis and Quantization Functions

- Adaptive Codebook Functions

- Fixed Codebook Search

- Discontinuous Transmission (DTX)

- Post Processing

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