Method for calculating HMM output probability and speech recognition apparatus

Abstract

The invention enables even a CPU having low processing performance to find an HMM output probability by simplifying arithmetic operations. The dimensions of an input vector are grouped into several sets, and tables are created for the sets. When an output probability is calculated, codes corresponding to the first dimension to n-the dimension of the input vector are sequentially obtained, and for each code, by referring to the corresponding table, output values for each table are obtained. By substituting the output values for each table for a formula for finding an output probability, the output probability is found.

1 . A speech recognition apparatus, comprising: 
 a characteristic analyzer which performs characteristic analyses on an input speech signal and which outputs an input vector at each point of time and components composed of a plurality of dimensions;    a scalar quantizer which replaces the components by predetermined codes by performing scalar quantization on received components for the dimensions from said characteristic analyzer;    an arithmetic processor which finds an output probability by using output values obtained by referring to tables which are created beforehand and uses the output probability to perform the arithmetic operations required for speech recognition; and    a speech-recognition processor which outputs the result of performing speech recognition based on the result of calculation performed by said arithmetic processor,    said tables being created for sets formed such that among the first to n-th dimensions, dimensions capable of being treated as each set are collected, and in the table for each set, output values, found based on codes selected for the dimensions existing in the set, being found as total output values for combinations of all the codes, and the combinations of the codes are correlated with total output values obtained thereby; and    based on the codes selected for the dimensions corresponding to one set, by referring to said tables, said arithmetic processor obtaining the total output values which correspond to the combinations of the code for the dimensions and calculating the output probability based on the total output values.    
   
   
       2 . The speech recognition apparatus as set forth in  claim 1 , when the numbers of codes in the dimensions in collections of the dimensions capable of being treated as each set are allowed to differ, dimensions having identical numbers of codes being collected to form each set.