OPTICOM OPERA - V 3.5 User Manual page 62

Delay and Gain
Compensation
C H A P T E R 4 : G E T T I N G
F R A M E W O R K
The following step "Delay and Gain Compensation" is as complex as some
perceptual algorithms are themselves, especially if a robust and computational
efficient implementation is required. Special care has to be taken to treat varying
delays as they might occur due to missing synchronization of the input signals,
or for instance with Voice over IP connections. As a result of the delay
compensation, time aligned signals will be provided, together with values that
are suitable to characterize the delay which was introduced by the device under
test.
Gain compensation is also mandatory. A level difference between the two input
signals will be clearly perceptible in an A/B comparison test but usually it is not
intended to be measured as a degradation of the sound quality. Nevertheless,
the information that such a gain difference exists and its measured value, may
be an important information for the user.
Other features required by a modern measurement tool like OPERA™ are means
to generate a test signal (to be seen on the top of Figure 4.22), to remote
control the system (Remote Control), and also to control it by other programs
and scripts (Scripting Interface). Scripts written in an easy to learn macro
language (e.g. VBScript, Java Script etc..) will allow for unattended, automated
measurements. From the user's point of view it is also desirable that there is a
convenient way to copy measurement results and graphs into other documents,
and to facilitate the publication, documentation and interpretation of the results.
File
AES/EBU
Test Signal
Analog
Generation
POTS a/b
ISDN (S0)
File
AES/EBU
Analog Input 1
POTS a/b
ISDN (S0)
File
AES/EBU
Analog
Input 2
POTS a/b
ISDN (S0)
Remote Control
Network
Figure 4.22: Block diagram of the OPERA™ measurement system
As Figure 4.22 illustrates, the measurement algorithm itself is only a very
small part of the entire measurement system. It is obvious that a variety of audio
processing algorithms will require the same input handling, filtering, delay
compensation and a similar user interface.
T O K N O W T H E
File
DC Filter
Delay and Gain
Compensation
DC Filter
Controller
Scripting Interface
File
56
O P E R A ™
Measurement
Results
Algorithm
Graphical or
Textual
Representation
User Interface
Screen
User
Archive