Speech recognition is one of the most indispensable technologies for human to realize a highly intelligentized and fully roboticized information society in the future, With many researchers' enormous efforts, the past tens of years has witnessed significant progress in speech recognition technologies and part of them have already been applied in people's daily life. The technologies of small or medium vocabulary speech recognition,, such as voice command recognition, keyword spotting and continuous digit string speech recognition, are of great importance in the application-oriented study of speech recognition. In this paper we focus our research on Mandarin OOV spotting and keyword spotting. There are several points in my work: 1. Because the existence of OOV words makes bad effect on the performance of speech recognizer, we studied different OOV rejection approaches to reject OOV word. Meanwhile, we compare the performance of these approaches. 2. Investigate some aspects of keyword spotting technology and build a basic system of Mandarin keyword spotting. We use atonal syllables as filler models for non-keywords and implement frame synchronous Viterbi-Beam search based on lexical tree. 3. Make introductions to the speech recognition projects I was involved in these years and the problems we meet in the projects.
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