Abstract
Problem statement: Dialects of Thai are quite different in the speaking styles. Environmental noises play an important role in corrupting the communication speech quality. Two factors affect the coded speech in the present speech communication. It is necessary to investigate how the two factors influence on the speech compression. Approach: In this study, the Multi-Pulse based Code Excited Linear Predictive (MP-CELP) coder and the Conjugate Structure Algebraic Code Excited Linear Predictive (CS-ACELP) coder are selected as the coding methods. This study shows the effects of the six kinds of noise to speech coding quality. The comparison of speech quality of the four coded Thai dialects is conducted. The speech material includes a hundred male speech utterances and a hundred female speech utterances. Four speaking styles include Thai Northern, North Eastern, Southern and Central dialects. Five sentences of Thai speech are chosen. Six types of noise include train, factory, motorcycle, air conditioner, men speaker and women speaker. Moreover, five levels of each type of noise are varied from 0-20 dB. The subjective test of mean opinion score are exploited in the evaluation process. Results: The experimental results show that CS-ACELP gives better speech quality than that of MP-CELP at all three bitrates of 6000, 8600 and 12600 bps. When considering the levels of noise, the 20-dB noise gives the best speech quality, while 0-dB noise gives the worst speech quality. When considering the speech gender, male speech gives better results than that of female speech. When considering the types of dialect, the central dialect gives the best speech quality, while the North dialect gives the worst speech quality. Finally, when considering the types of noise, the air-conditioner noise gives the best speech quality, while the train noise gives the worst speech quality. Conclusion: From the study, it can be seen that coding method, type of noise, level of noise, speech gender and dialect influence on the coding speech quality.
Highlights
Of the traffic occupancies depending on the type and number of users
This study proposes a study of the quality of speech coding based on the practical application which considers the communication environment with various types of background noises
They are subsequently converted to Line Spectrum Pairs (LSP) and quantized using
Summary
Of the traffic occupancies depending on the type and number of users. Speech compression is expected to. Their speaking rates are varied, that is, the Northern dialect’s rate is rather slow, while the Southern dialect’s is the quickest rate among those four dialects. The flexibility in the coding rate is necessary to support the surge Fig. 1: Block diagram of noisy communication channel To overcome this problem, a bitrate-scalable speech coder has been developed where the received speech signal can be decoded from the received packets, which contain only some of the whole encoded packets. We considered the dialects of Thai speech with different Fig. 3: Block diagram of CS-ACELP decoder speaking styles that may cause different speech quality with the same coding algorithm. Linear Prediction (LP) analysis is done every 10 ms frame to compute the
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