Patent ID: 6741962
Filing Date: 2004-05-25
Classification: G10L

Abstract:
A speech recognition system for recognizing an input voice of a narrow frequency band, said speech recognition system including:a power spectrum calculating unit for calculating power spectrums of said input voice of said narrow frequency band; a frequency band converting unit for converting said input voice of said narrow frequency band into a pseudo voice of a wide frequency band which covers an entirety of said narrow frequency band and which is wider than said narrow frequency band, said frequency band converting unit comprising: i. a eigen-vector storing unit for storing a plurality of eigen vectors of power spectrums of said wide frequency band pseudo voice; ii. an expansion coefficient calculating unit for calculating expansion coefficients that said power spectrums calculated by said power spectrum calculating unit are expanded by a linear combination of said plurality of eigen vectors; iii. a frequency band expansion unit for calculating additional power spectrums in a lack frequency band by use of said expansion coefficients calculated by said expansion coefficient calculating unit, where said lack frequency band is covered by said wide frequency band but not covered by said narrow frequency band, and said frequency band expansion unit combining said additional power spectrums in said lack frequency band into said power spectrum of said narrow frequency band calculated by said power spectrum calculating unit to prepare pseudo power spectrums of said pseudo voice of said wide frequency band; and iv. a melcepstrum calculating unit for calculating a melcepstrum characteristic quantity based on said pseudo power spectrum prepared by said frequency band expansion unit; a pattern reference unit for receiving an output from said frequency band converting unit and comparing said output with a standard pattern for carrying out the speech recognition; a standard pattern preparation unit for receiving an output from said frequency band converting unit and preparing the standard pattern based on said output for carrying out the speech recognition; and a standard pattern storing unit for storing the standard pattern prepared by the standard pattern preparation unit for allowing said pattern reference unit to compare said output with said standard pattern.