VCS VideoJet X.21, Manual

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Configuration with the NCTerminal Software
52
VideoJet X.21/G.703
Manual
Audio Settings
Bidirectional audio transmission is possible with the
VideoJet
X.21/G.703
system. This is useful for security applications such
as acoustic surveillance and announcements through to the object
of surveillance. Audio transmission can also be used for other appli-
cations, such as door intercom systems.
Because audio data and video data are transmitted in parallel along
the same line, both data flows share the available line capacity.
When audio transmission is activated, the data rate for moving
images is reduced to that of the audio data rate which can result in
reduced video quality (lower frame rate and/or reduced image res-
olution).
VideoJet X.21/G.703
offers several configuration
options to provide the optimum solution for each application, which
are described below.
Various coding methods are available for audio transmission which
differ in terms of audio quality, complexity and the required data
rate. A comparison of the various methods is given in the table
below:
Tab. 5-3 Audio Coding Method
The overview above shows that the G.728 standard offers the same
audio bandwidth as G.711 in spite of a reduced data rate. The audio
quality will, however, be somewhat reduced, which may be notice-
able in the transmission of music.
In order to achieve a good audio transmission quality, adaptation of
the audio level to the external components used is necessary:
Standard Method Bandwidth Data rate
G.711 PCM 3.1 kHz 56 Kbit/s
G.728 LD-CELP 3.1 kHz 16 Kbit/s