Patent EP-0138071-A2 (EP)
Title: Method of determining the excitation condition of a speech segment with an application to automatic speech recognition
Inventor: HOGE HARALD DR
IPC: G10L25/93
Filed: 1984-09-13
Abstract: 1. A method of excitation analysis for automatic speech recognition, wherein a signal parameter extraction from the speech signal which is to be recognised is carried out in a first extraction stage of a recognition system, and a feature specification and classification of the obtained features by comparison of predetermined features of the vocabulary of the recognition system are carried out and in a second extraction stage of the recognition system, and to specify the excitation state, namely either "voiced" (Z1 ), "unvoiced" (Z2 ) or "pause" (Z3 ) in the second extraction stage of the recognition system, selected parameters are obtained in the first excitation stage, namely the parameter for the nergy of the speech band (P1 ), the voicing parameter (P2 ) and the parameter for the spectral energy ratio (P3 ), characterised in that an auxiliary parameter (P4 ) for a relative energy is defined firstly from the parameter for the energy of the speech band (P1 ) and from the voicing parameter (P2 ), where the auxiliary parameter (P4 ) forms the ratio of the energy (P1 ) of the current speech signal to an intermediate value of the energy (E), which itself represents a gauge of the energy of the speech signal in voiced zones, that the parameters (P1 , P2 , P3 , P4 ) are then logic-linked in a logic-linking function unit in accordance with a predetermined logic-linking plan such that one of the three excitation states is characterised by the respective excitation state parameter (Z1 , Z2 or Z3 ), for which purpose a transformation of input signals (xi ) to output signals (yi ) of these function elements takes place prior to the logic-linking with the assistance of a specified function element, where the parameters (P1 , P2 , P3 , P4 ) function as input signals and where the output signals are the signals which are to be logic-linked, that the auxiliary parameter (P4 ) is generated by firstly comparing the voicing parameter (P2 ) with an empirically-determined constant (C1 ), that in the event that the voicing parameter (P2 ) is greater than the constant (C1 ) the intermediate value of the energy (E) is multiplied by a likewise empirically-determined further constant (C2 ) in order to form a new intermediate value (E), that the parameter for the energy (P1 ) is compared with the new intermediate value (E), that in the event that the parameter for the energy (P1 ) being greater than the new intermediate value (E) the intermediate value (E) assumes the value of the parameter for the energy (P1 ), that in the event that the parameter for the energy (P1 ) is not greater than the new intermediate value (E) the new intermediate value (E) for the energy is retained, that in the event that the voicing parameter (P2 ) is not greater than the constant (C1 ) the original intermediate value (E) for the energy remains unchanged, and that the value for the auxiliary parameter (P4 ) is specified as the difference between the valid intermediate value (E) for the energy and the parameter for the energy (P1 ).