Field Report: Audio TX Multiplex

Every so often, a new product is introduced that makes people ask themselves "Why didn't I think of that?" Products that, at the time they were made available, were revolutionary because they filled a need we did not realize existed. In time, these products evolved from something we didn't know we needed to something we now can't do without. Hard-disk editors, compact interfaces and DTMF-accessible remote control systems are all examples of items introduced during my career that filled such a need. I have one more to add to the list: MDO UK's Audio TX Multiplex.

The Audio TX Multiplex application provides the ability to broadcast multiple audio channels over a LAN. A workstation/desktop/routing switcher, if you will. The concept is simple. With a single PC with a static IP address installed in a rack room or master control, audio provided as an input can be monitored from any LAN workstation on the network.

As expected, the setup and configuration is accomplished in two parts, the server/encoder and the workstation/decoder. The server can encode one stereo input or two mono channels using a single Sound Blaster card up to 48 stereo inputs, or 96 mono channels using more elaborate multi-channel audio cards. In fact, any combination of stereo and mono channels can be used, based on individual needs. The user can individually configure each input's sample rate from 16kHz to 48kHz, compression type from linear to MP2 to MP3 and select from various bit rates. The design of the software makes the setup and configuration of the input channels extremely easy. In fact, it wasn't until after I had the system running that I fully read the documentation. The application is virtually self-explanatory.

System spec

Our test machine was a P4 1.8GHz running a Motu 24 I/O Interface. This interface provides 24 mono analog inputs or 12 stereo inputs or any combination in between. The manufacturer states that a P4 2GHz system is capable of running about 35 mono channels or 25 stereo channels. During the peak of testing we were running 15 inputs (eight mono and seven stereo). On the server's display, a small bar graph displayed the CPU load generated by the application. On our test machine we registered a peak of 51 percent, so you can probably count on needing a powerful PC if more than one 24 I/O is used. However, even at 51 percent we never encountered any audio dropouts while listening.

The efficiency of the streams is another plus. In an effort to minimize the bandwidth impact on a LAN, the Audio TX Multiplex uses multicast technology. This allows the server to transmit a single copy of an audio channel regardless of the number of clients listening. With several clients listening, monitoring our 100Mb/s switch indicated only a minimal impact on network bandwidth. Even when opening a 150MB Power Point presentation across the network, the audio playback was not interrupted.

Moving on to the workstation, I was amazed to see the planning and thought that went into this application. Installation and configuration of the client software is fool proof. Enter the server's IP address into a Web browser and a Web page appears that provides two links. The first installs the client software; the second configures the client with the server's IP address and enters the appropriate IP address. The operation of the client is just as easy. Opening the application provides a small desktop interface about the height of a Windows title bar. It has just enough room for a pull-down list to select the desired channel, audio meter and a slider for volume. If the small desktop interface gets in the way it can be minimized, leaving only the audio.



The Receiver Bar occupies little space on the desktop. The drop-down provides instant access to available channels.

At this point you're probably asking “What do I use it for?” You would be surprised where this can be useful. For an FM station, you might benefit from having not only your on-air audio, but also that of your closest competitors as well. These, in addition to your production studio's program audio bus, would give program directors the ability to monitor your station, sample the station across town or approve daily promos or imaging production without leaving his desk. The sales manager could listen and approve spot production without coming to the studio. A news/talk facility can really exploit the potential uses. In addition to the feeds listed above, think about adding feeds such as NOAA, news feed satellite channels, local TV audio or even a national cable channel's audio. Would your news director benefit from the ability to listen to the news cue feed right in his office? Perhaps your sports director would like to have the ability to listen to a press conference. You can see where the possibilities are almost endless.

It has been said, “simplicity is the hallmark of genius.” If so, this application comes close to the level of genius. Its installation and operation is as streamlined as could ever be expected. Yet, its functionality is nearly endless. Now that PCs with speakers are commonplace in the office, Audio TX Multiplex could be a valuable addition to most any broadcast facility, big or small.


Arnaut is the broadcast IT engineer for WJR, WDVD and WDRQ Radio, Detroit, MI.

Performance at a glance

Ease of installation
Quality audio with basic PC
Web browser-based client installer
Efficient use of network resources
Ability to customize audio settings
Unlimited number of audio channels

Audio TX

P +44 121 256 0200
F +44 121 256 5109
W www.audiotxmultiplex.com
E sales@audiotx.com


Editor's note: Field Reports are an exclusive Radio magazine feature for radio broadcasters. Each report is prepared by well-qualified staff at a radio station, production facility or consulting company.

These reports are performed by the industry, for the industry. Manufacturer support is limited to providing loan equipment and to aiding the author if requested.

It is the responsibility of Radio magazine to publish the results of any device tested, positive or negative. No report should be considered an endorsement or disapproval by Radio magazine.


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