Speech recognition system, method for recognizing speech and electronic apparatus

A speech recognition system recognizing speech uttered in a noise environment on a registered phrase-by-phrase basis, comprising:

• a speech characteristic-amount calculation unit that calculates an amount of speech characteristics of each phrase in the uttered speech;
• a phrase storage unit that stores speech pattern sequence information of phrases;
• a likelihood value calculation unit that calculates likelihood values of a plurality of speech recognition candidates by comparing the amount of speech characteristics of a phrase calculated by the speech characteristic-amount calculation unit with the speech pattern sequence information of a plurality of the phrases stored in the phrase storage unit;
• a candidate extraction unit that, based on the likelihood values calculated by the likelihood value calculation unit, selects, in decreasing order of the likelihood values, a first speech recognition candidate, a second speech recognition candidate ranked lower than the first speech recognition candidate, and a third speech recognition candidate ranked lower than the second speech recognition candidate;
• and
• a recognition filtering unit that determines whether to reject or not reject the speech recognition candidates extracted by the candidate extraction unit based on the likelihood difference ratio between the difference in likelihood values between the first speech recognition candidate and the second speech recognition candidate and the difference in likelihood values between the second speech recognition candidate and the third speech recognition candidate.

A method for recognizing speech uttered in a noise environment on a registered phrase-by-phrase basis, comprising the steps of:

• calculating an amount of speech characteristics of each phrase in the uttered speech;
• calculating likelihood values of a plurality of speech recognition candidates treated as targets to be subject to speech recognition by comparing the amount of speech characteristics calculated for a phrase with speech pattern sequence information of a plurality of phrases stored in advance;
• selecting a first speech recognition candidate, a second speech recognition candidate ranked lower than the first speech recognition candidate, and a third speech recognition candidate ranked lower than the second speech recognition candidate in decreasing order of the likelihood values based on the likelihood values calculated for each phrase;
• comparing a likelihood difference ratio between the difference in likelihood values between the selected first speech recognition candidate and the selected second speech recognition candidate and the difference in likelihood values between the selected second speech recognition candidate and the selected third speech recognition candidate;
• and
• determining, when the likelihood difference ratio is lower than a predetermined value, to reject the first speech recognition candidate, and when the likelihood difference ratio is higher than the predetermined value, to regard the first speech recognition candidate as a target to be subjected to speech recognition.

An electronic apparatus comprising a speech recognition system that recognizes speech uttered in a noise environment on a registered phrase-by-phrase basis, wherein

• the speech recognition system comprises:
• a speech characteristic-amount calculation unit that calculates an amount of speech characteristics of each phrase in the uttered speech;
• a phrase storage unit that stores speech pattern sequence information of phrases;
• a likelihood value calculation unit that calculates likelihood values by comparing the amount of speech characteristics of a phrase calculated by the speech characteristic-amount calculation unit with the speech pattern sequence information of a plurality of the phrases stored in the phrase storage unit;
• a candidate extraction unit that, based on the likelihood values calculated by the likelihood value calculation unit, selects a plurality of speech recognition candidates in decreasing order of the likelihood values;
• and
• a recognition filtering unit that determines whether to reject or not reject the speech recognition candidates selected by the candidate extraction unit based on distributions of the likelihood values of the selected speech recognition candidates, and
• the electronic apparatus comprises a control unit that controls the electronic apparatus to perform a predetermined operation based on the speech recognized by the speech recognition system.