Communication Via a Software Codec
MDO Develops Communicator to Bypass Hardware-Based
Codecs
by Lawrence Hallett
The Communicator software ISDN and IP audio codec is the first
product in the AudioTX range
from MDO UK.
Designed for such tasks as remote linking into studios, the
software is suitable both studio PC and laptop use. This makes it
ideal for reporting and outside broadcasts, where it is essential to
get high-quality audio from a remote location to air with a minimal
amount of technical equipment.
By using the software on a laptop PC with input devices such as
microphones, CD or MiniDisc, we can avoid the need for a separate
hardware codec and physical audio mixer.
Self-contained package
Users can handle recording, preproduction, mixing and signal transmission
with a simple, self-contained package - all that is needed is an
ISDN or other digital connection.
Designed for broadcast, professional audio and telecommunications
applications and running under Windows 98 or NT/2000 PCs, the
Communicator can connect to ISDN audio codecs including the Musicam
USA CDQ Prima, Telos Zephyr and GlenSound and Dialog4 units.
The Communicator uses a proprietary autoconnect algorithm
automatically to detect the type of codec at the other end of the
line and configure itself.
Both 64 kbps and 128 kbps connections are possible ó using one
or two ISDN B channels - and coding algorithms available include
MPEG Layer II and Layer III in mono/stereo/joint stereo modes; G.722
as 7.5 kHz speech only and G.711 as 3.1 kHz for telephony use.
If an ADSL, DSL, cable modem or leased-line Internet connection
is available, the system can make a live audio connection over the
Internet.
According to the manufacturer, when using ADSL or a cable modem,
a typical achievable data bit rate will be approximately 20 percent
less than the maximum achievable bit rate of the connection itself
in its slowest direction - either upstream or downstream.
The actual throughput will depend on the setup of the ADSL or
cable modem connection being used. However, with sufficient
capacity, connection modes can include uncompressed PCM linear audio
in mono or stereo modes, MPEG Layer II in mono/stereo/joint stereo
modes at up to 384 kbps and MPEG Layer III in mono/stereo/joint
stereo modes at up to 320 kbps.
Excellent flexibility
The Communicator can operate over Ethernet or private wide-area
networks.
Using a standard PC network card or other installed networking
hardware, the AudioTX Communicator can provide live audio links over
IP networks. Using existing installations of hubs and routers makes
the scale of a given network irrelevant.
By default, the system uses a standard IP network port, though it
is possible to alter this to suit local network configuration
practices.
The Communicator will run over private leased lines, using
existing IP or an external device that provides Ethernet connection
over the circuit concerned.
Larger organizations can use the software over ATM or other
large-scale telecom networks.
Using existing networking setups in the PC on which the software
is installed gives excellent flexibility. A standard network card
plugged into an Ethernet connection to the ATM network is
required.
Specialized ATM hardware can be employed, provided it presents an
IP network connection capable of carrying TCP packets to/from the PC
concerned. For such private and wide area networks, the connection
modes available are the same as those available for ADSL or cable
modem installations.
The Communicator is designed to work with most good-quality PC
soundcards, provided that the card supports full-duplex audio and
operates at 44.1 kHz or, ideally, 48 kHz.
Test circuit
Performance will be limited if the card produces electrical "crackles"
or exhibits high levels of background noise during operation. At
the AudioTX Web site, the manufacturer
posts a list
of cards recommend for use with AudioTX Communicator.
The software will operate with any ISDN terminal adaptor that
meets the Common ISDN Application Program Interface 2.0
specification or with a suitable Ethernet, cable modem or ADSL
connection, as circumstances dictate.
Because the CAPI 2.0 standard can be somewhat loosely interpreted
in some designs, MDO UK recommend sticking with one of the two biggest
brands of TAs - AVM or Eicon.
For the purposes of this review, the software was tested over
ISDN circuits after installation on an 800 MHz Athalon PC with 256
MB RAM, running Windows 98SE. The PC was fitted with a PCI bus ISDN
TA and a Marc 2 soundcard.
MDO UK said it tested the software on a variety of PCI, ISA, USB
and PCMCIA ISDN TAs, but that because of their inherently limited
data throughput capacity, serial port ISDN devices cannot be used
with the software.
The minimum recommended specifications are a 300 MHz Pentium II
with at least 64 MB RAM (reduced to 32 MB for a Windows 98
installation).
Clear metering
Using a standard ISDN connection at 64 and 128 kbps, MPEG Layer
II connections in mono and joint-stereo were made with both the
software suppliers and to the studios of KISS100 FM in London.
Tests also utilized the G.722 and G.711 modes. Operation of the
AudioTX Communicator is straightforward: Simply enter the number
to connect to then select the coding algorithm and the appropriate
data-rate for the type of connection required. This is then stored
in the phonebook so next time it is just a matter of selecting the
entry again and clicking the dial button.
Audio metering is done through a set of LED-style meters, which
offer fast-acting peak VU-style metering coupled with PPM-style
level metering.
The download software
requires the purchase of an unlock code to remove the connection
duration limitations of the trial mode installation. The software
unlock is machine-specific; for purchasers wanting to move the software
between machines, a USB or parallel port dongle-controlled version
is available. The dongle-controled license is the option recommended
by MDO UK.
Installation was quick. The software recognized the previously
installed ISDN board and soundcard and did not require a reboot
before becoming operational. MDO UK recommends that the Communicator
be used on a PC running, in order of preference, under Windows XP
or 2000, Windows NT or Windows 98. The reason that Windows 2000
or NT are preferred is their ability to keep individual processes
separate when multitasking.
Framing problems solved
The importance of this became apparent during the testing when,
running Windows 98, there were problems with the "framing" of the
datastream, resulting in interruptions to and distortion of the
audio being transmitted and received.
The reason for this distortion was the presence of a background
task running on the Windows 98 that conflicted with the resource
demands of the codec software.
I solved the problem by switching off virus checkers and other
System Tray tasks. On a Windows 98 machine, trying to do a live,
real-time, program mix and using the Communicator software at the
same time could lead to problems.
With the proviso that some engineers might feel the software is
lacking in connection progress and analysis information, the AudioTX
Communicator operates well on a correctly configured PC.
It will be interesting to see what other products are introduced
into the range over the coming months.
Lawrence Hallett reports on the industry for Radio World from
Norwich, England.
For information from MDO UK, contact Mo Dutta in England at
telephone: +44-121-248-0200; FAX: +44-121-248-5109; e-mail: mo@mdouk.com or visit http://www.audiotx.com// on the World Wide Web.
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