COMPUTATION AND QUANTIZATION OF VOICED EXCITATION PULSE SHAPES IN LINEAR PREDICTIVE CODING OF SPEECH

摘要

The invention facilitates linear predictive coding of voiced speech sounds, with a single voiced excitation code book encompassing a wide range of different pitch periods. Unlike prior art techniques which represent voiced excitation using fixed pulse shapes with random variations added, the invention uses a single code book of representative frequency spectra to closely match the original unquantized pulse shape. In particular, the invention facilitates determination of a pulse shape vector v for a linear predictive speech coder from a voiced residue pulse u, during a sampling instant n characterized by a gain g and a pitch period p. A spectral magnitude vector Suq of dimension dsm is derived (38) to represent the frequency spectral magnitude of the pulse during the sampling instant. A code book Csm (46) containing a plurality of vectors representative of pre-selected spectral magnitude vectors is provided. A vector which provides a minimum error approximation to Suq is selected from the code book (40). ism is the spectral magnitude index, within the code book, of the selected minimum error approximation vector. A quantized spectral magnitude vector S having the spectral magnitude index ism and having dsm elements is then derived (42). A complex frequency spectrum signal X is derived from S and is converted to a complex time-domain representation x. The pulse shape vector v is then derived from the Real components of x.