This study was designed to evaluate the
voice quality of VoIP referring to packet loss
rates of 0%, 2%, 6%, 10% and 20%
approximately, with G.729 codec and G.711
(A-law) codec. Therefore, there were ten
conditions to test. Following [25], each
condition has been conducted with at least 24
inexperienced subjects/participants or at least
240 inexperience subjects/participants
totally, who were science and technology
students, Thai native speakers, in KMUTNB.
They had few criteria of homogeneity which
only consisted of the range of age,
nationality, and the background of education
(based on science and technology in the
same university).
The method for voice quality evaluation
is conversation-opinion tests, using paper
based Richard’s task, following ITU-T
recommendations. The advantages of
conversation-opinion tests are reaching the
realism and obtaining two sets of data per
round of tests [13].
However, each condition has been tested
by about 30 subjects/participants due to
some data classified as outliers (e.g.
distinguishable high or low scores comparing
to the majority), to validate the gathered
data.