VoIP quality of experience: A study of perceptual voice quality from G.729, G.711 and G.722 with Thai users referring to delay effects

This paper presents the conduction of conversational tests with three codecs; G.729, G.711 and G.722 referring to different one-way delays of <;10 ms, 400 ms and 800 ms, to help investigate delay effects to perceived voice quality by Thai users. The result from this study is found that with the best condition of delay (<;10 ms delay), the delay of 400 ms and 800 ms, the observed difference among three codecs was not statistically significant. Also, it has been found that Thai users did not detect a statistically significant difference of perceived voice quality from the same codec (G.729, G.711 or G.722) among three delay conditions of <;10 ms, 400 ms and 800 ms. This result is not consistent with the ITU-T standard because ITU-T recommended that the delay of 400 ms and above is unacceptable. The possible reasons could be language and cultural effects, which should be investigated in future.