Features |
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Bidirectional 7.5 kHz audio
at 56/64 kb/s. |
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Bidirectional 15 kHz audio
at 112/128 kb/s. |
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Very low delay for real-time
cueback. |
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Compatible with other G.722
codecs. |
| The
DXP.1 and DXR.1 are digital audio compression devices designed
for broadcasters. |
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They employ the
ITU G.722 international standard to send and receive 7.5 kHz
audio at transmission |
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rates of 56/64 kb/s. |
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These new models also provide
a full 15 kHz bidirectional feed on 112/128 kb/s circuits, such
as BRI ISDN, fractional T1 or satellite links. |
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The DXP.1 is compact and
portable, with adjustable headphone output and an input switchable
between |
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microphone and line levels. |
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The DXR.1 is rack mountable,
with balanced, line level input and output. |
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Proper input levels and sync
status are indicated on the front panels of both models. |
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A service unit or terminal
adapter is needed to interface these codecs to your data circuit.
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DB25 (25 pin) connectors
using the EIA530 protocol are included as a standard data port. |
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An optional cable converting
EIA530 to X.21 or V.35 is available. |
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Digital Services |
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Both the DXP.1 and the DXR.1
work on any synchronous 56, 64, 112 or 128 kb/s digital transmission |
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system, including ISDN, Switched
56, Dedicated Digital Service (DDS), Fractional T1, digital
satellite |
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links, and wireless modems. |
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For part-time audio feeds,
dial-up BRI ISDN or Switched 56 digital lines are ideal since
they are billed at |
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a low monthly cost, plus
per minute usage which is not much more than standard analog
lines. |
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Basic Rate Installation (BRI)
ISDN is available throughout the world. SW56 is a North American
|
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"precursor" to
ISDN and both services work with one another. |
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Applications |
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The DXP.1 and DXR.1 provide
a cost saving alternative to satellite feeds or dedicated circuits. |
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They are ideal for applications
requiring high quality (7.5 or 15 kHz) mono audio. |
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Since they have very little
processing delay, these codecs are the best choice for live
programming |
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such as talk, news, and sports,
where real-time cueback is essential. |
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Other applications include
network distribution, studio-to-studio links, and STLs. |
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Also, since G.722 is an international
telephony standard, these Comrex codecs provide compatibility
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with a large established
base of users worldwide. |
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Technical |
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Pulse code modulation, used
by most digital audio devices, requires large amounts of bandwidth
|
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(or high data rates) for
transmission. |
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Techniques have been developed
to eliminate redundant information carried within the digitized
bit |
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stream. |
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Among the most popular of
these is Adaptive Differential Pulse Code Modulation (ADPCM). |
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|
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The G.722 algorithm employed
in the DXR.1 and DXP.1 is an international ITU standard which
uses |
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ADPCM to achieve a 4:1 data
reduction, allowing more audio information (or wider bandwidth)
to be sent |
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along a DS0 digital channel. |
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|
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Both the DXP.1 and the DXR.1
incorporate 64X oversampled Sigma Delta Analog to Digital and
Digital to |
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Analog converters. |
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The G.722 Algorithm is run
on two ADSP-2101 Digital Signal Processors. |
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They use a statistical synchronization
technique which is continually updated by the decoder. |
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Audio is sampled and reconstructed
at 16 kHz (7.5 kHz mode) or 32 kHz (15 kHz mode) with 16 bit
|
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quantization. |
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These codecs automatically
adapt to 56, 64, 112, or 128 kb/s transmission channels. |
Connections