Telephony Band Voice Quality Testing; What To Know About Testing Telephony Band Voice Quality - OPTICOM OPERA - V 3.5 User Manual

C H A P T E R 6 :
6 TELEPHONY BAND VOICE
QUALITY TESTING
Applying the Perceptual Speech Quality Measure
(PSQM) and others to Voice Signals in a
Telecommunication Environment.
C
hapter 4 dealt with the general operation of the OPERA™ framework.
This chapter is about all the specific concerns in assessing telephony
band voice quality. In addition, the fundamentals of the corresponding
measurement methods will be described. Finally, some measurement
examples at the end of this chapter will help with your first measurement
applications.
6.1 What To Know About Testing
Telephony Band Voice Quality
Subjective quality assessment of speech codecs is one of the key technologies in
designing digital telecommunication networks. Recommendation P.830 defined
subjective testing methodologies for speech codecs. Since subjective quality
assessment is time-consuming and expensive, it was therefore desirable to
develop an objective quality assessment methodology to estimate the subjective
quality of speech codecs with less subjective testing.
In the past, the most widely-used objective speech quality measure was the
Signal-to-Noise Ratio (SNR = S/N). However, it was pointed out that the SNR
does not adequately predict subjective quality for modern network
components. This is especially true for recent low bit-rate codecs.
Within the telecommunication sector of the ITU, in 1996 study group 12
finalized recommendation P.861 [ITUT861] for the objective analysis of speech
codecs. After a wide-ranging comparison of proposed methods, the group opted
for the PSQM algorithm. PSQM correlated up to 98 percent with the scores of
subjective listening tests. This high correlation was excellent in 1996 and still is
extraordinarily good, however, as soon as PSQM is applied to signals that are
out of the scope of the recommendation, the correlation will usually drop down
significantly. This is mainly due to the fact that the coding and network
technology has dramatically changed since the time PSQM was developed.
One of the key technologies that demand different measures is Voice over IP
(VoIP). Although the PSQM implementation in OPERA circumvents the major
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