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C H A P T E R
6 :
DefaultRefFileMixed.wav
DefaultRefFileMixed-a.wav
For measurements on analog lines it does not matter if a-law or mu-law coded
files are used, since they will be converted analog in any case. For ISDN, E1 or
T1 interfaces however the coding must be chosen conforming to the network
requirements. All reference files conform to P.800. Instead of the delivered files,
any other speech file may be used as well.
6.3 PSQM as an Example for Perception
Based Measurement Algorithms
The objective of PSQM is to mimic the sound perception of subjects in real-life
situations [BEER94]. PSQM simulates experiments in which subjects judge the
quality of speech codecs. This is done by comparing a coded signal
(characterized as output y[t] in Figure 6.1) to a source signal (input x[t]). For
this reason, experimental parameters – subject properties and listening
conditions – have to be taken into account. These parameters are the listening
level, the weighting on silent intervals, environment noise in the receiving side,
characteristics of the hearing threshold and finally the sending and receiving
characteristics of the handset.
Figure 6.1: Overview of the basic philosophy used in the development of the PSQM algorithm [ITUT861]
To the extent that PSQM is a faithful representation of human perception and
judgement processes, signals with inaudible differences between input and
output will receive the same PSQM score. In particular, if the input and the
output are identical, PSQM will predict perfect quality irrespective of the quality
of the input signal.
Within PSQM, the physical signals constituting the source and coded speech
are mapped onto psycho-physical representations that match the internal
representations of the speech signals (the representations inside our heads) as
closely as possible.
T E L E P H O N Y
B A N D
T E S T I N G
119
V O I C E
Q U A L I T Y
Mix
of
different
contents
was
selected
linguistic criteria, male and female
speaker, mu-law.
Same as DefaultRefFileMixed.wav but
a-law
languages.
The
following
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