Language Model Optimization for a Deep Neural Network Based Speech Recognition System for Serbian
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This paper presents the results obtained using several variants of trigram language models in a large vocabulary continuous speech recognition (LVCSR) system for the Serbian language, based on the deep neural network (DNN) framework implemented within the Kaldi speech recognition toolkit. This training approach allows parallelization using several threads on either multiple GPUs or multiple CPUs, and provides a natural-gradient modification to the stochastic gradient descent (SGD) optimization method. Acoustic models are trained over a fixed number of training epochs with parameter averaging in the end. This paper discusses recognition using different language models trained with Kneser-Ney or Good-Turing smoothing methods, as well as several pruning parameter values. The results on a test set containing more than 120000 words and different utterance types are explored and compared to the referent results with GMM-HMM speaker-adapted models for the same speech database. Online and offline recognition results are compared to each other as well. Finally, the effect of additional discriminative training using a language model prior to the DNN stage is explored.
KeywordsDeep neural networks Kaldi Serbian Language modeling MMI
. The work described in this paper was supported in part by the Ministry of Education, Science and Technological Development of the Republic of Serbia, within the project “Development of Dialogue Systems for Serbian and Other South Slavic Languages”, EUREKA project DANSPLAT, “A Platform for the Applications of Speech Technologies on Smartphones for the Languages of the Danube Region”, ID E! 9944, and the Provincial Secretariat for Higher Education and Scientific Research, within the project “Central Audio-Library of the University of Novi Sad”, No. 114-451-2570/2016-02.
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