Wide Band Audio Quality Testing; What To Know About Testing Wide Band Audio Quality - OPTICOM OPERA - V 3.5 User Manual

C H A P T E R 5 :
5 WIDE BAND AUDIO
QUALITY TESTING
Measuring the Perceived Audio Quality (PEAQ) of
e.g. MPEG Encoded Music Signals.
A
description of all specific concerns for assessing wide band audio
quality follows. In addition, the fundamentals of the corresponding
measurement method is explained. Finally, assistance with the first
measurement applications is provided at the end of this chapter.
5.1 What To Know About Testing Wide Band
Audio Quality
Audio quality is one of the key factors when designing a digital system for
broadcasting. The rapid introduction of various bit-rate reduction schemes has
led to significant efforts establishing and refining procedures for subjective
assessments, simply because formal listening tests have been the only relevant
method for judging audio quality in the past. As mentioned in Section 2.1, the
experience gained was the foundation for Recommendation ITU-R BS.1116,
which then became the basis for most listening tests of this type. This also
defines the applicability of wideband audio tests like PEAQ. They can be
applied wherever a subjective test according to BS.1116 would be applied. In
addition to that newer research shows that PEAQ can be applied instead of
MUSHRA tests as well, although this must be performed with special care.
Wideband audio does not mean that speech can not be assessed. However it
should be wideband speech in contrary to telephony bandwidth
(300...3500Hz). Otherwise algorithms like PESQ or PSQM are more
appropriate.
Since subjective quality assessments are both time-consuming and expensive, it
was beneficial to develop an objective measurement method to produce an
estimate of the audio quality. Traditional objective measurement methods, like
Signal-to-Noise-Ratio (SNR) or Total-Harmonic-Distortion (THD) have never
really been shown to relate reliably to the perceived audio quality. The
problems become even more evident when the methods are applied on
modern codecs that are both non-linear and non-stationary. After thorough
verification, a model was recommended by the ITU-R as a measure for the
perceived audio quality ("PEAQ") under recommendation BS.1387 in late
1998.
W I D E B A N D A U D I O
85
Q U A L I T Y T E S T I N G
5
Chapter