DISTRIBUTED RECOGNITION FOR CONTINUOUS SPEECH IN LARGE VOCABULARY BRAZILIAN PORTUGUESE / RECONHECIMENTO DISTRIBUÍDO DE VOZ CONTÍNUA COM AMPLO VOCABULÁRIO PARA O PORTUGUÊS BRASILEIRO

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

This Thesis aims at exploring several approaches for performance improvement of the Automatic Speech Recognition System with large vocabulary for the Brazilian Portuguese when applied in a distributed scenario (Distributed Speech Recognition). With this purpose, a speech database for continuous speech recognition for the Brazilian Portuguese with 100 speakers was constructed, each one uttering 1000 phonetic balanced sentences. The recording was carried out in a studio (environment without noise) with a specification of recording that would be able to allow the input of several speech codecs in Cellular Mobile Telephony and IP Networks, in particular the ITU-T G.723.1, AMR-NB and AMR-WB. In order to work properly, Automatic Speech Recognition Systems require that the recognition features be extracted at a high rate. However, the Speech codecs for Cellular Mobile Telephony and IP Networks normally generate its parameters at lower rates, which degrades the performance of the recognition system. Usually the linear interpolation in the LSF (Line Spectral Frequencies) domain is used to solve this problem. In this Thesis the accomplishment of the interpolation with the use of a Digital Filter Interpolator was proposed and demonstrated to have a higher performance than the linear interpolation in recognition systems. The use of the interpolated ISFs (Immittance Spectral Frequencies) was also evaluated as recognition feature, which had shown to be inadequate for this purpose, as well as the LSFs. Another very important aspect for the distributed speech recognizers is the recovery of lost packets, that has direct impact in the recognition performance. Normally the coders insert zeros in the lost packets or interpolate linearly the received packets aiming to restore them. A new technique based on Neural Networks was proposed in this thesis that showed to be more efficient in the restoration of these lost packets with the purpose of speech recognition.

ASSUNTO(S)

redes ip reconhecimento de voz distribuido distributed speech recognition redes neurais neural networks ip network

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