The Comrex Nexus has long been available in the USA and Canada, but now a Euro-ISDN version is available for use in the rest of the world. Housed in a compact, portable case, the Nexus provides mic/line input with an auxiliary tape input, headphone and line outputs, level and mixing controls, ISDN dialling, and a display panel to tell you what's happening. The built-in terminal adapter features BONDING, allowing the Nexus to be used in 128kbps mode for Comrex Turbo G.722 15kHz links with other Comrex Turbo G.722 codecs. 

The ability to store multiple ISDN line configurations makes the Nexus perfect for sports or any application where the codec will need to travel to different venues. The STL back-up mode makes this codec a great choice for low-cost "peace of mind." The Nexus is also ideal for news, weather or traffic delivery.

Also included is an ancillary data channel. This gives the user an additional data communications option. It can be connected to a computer, for messaging, such as call screening for a remote talk show or sending scores to a sports announcer.

*ISDN is a digital phone line which is ordered from the telephone company. The NExus is available in two versions: The North American "U" interface works in the United States and Canada. The International "S/T" interface works in most countries outside of North America.

Nexus is easy to use

• The intuitive user interface makes programming a cinch.

• The keypad and backlit LCD access simple menu options.

• One-button, quick-dial feature enables fast connections.

• The Nexus automatically adapts to 56, 64, 112 or 128 kb/s.

• Everything you need for bidirectional audio on ISDN is in one small 2.6 pound case, including the digital audio codec, terminal adapter (and NT1 in the North American version).

Nexus is full-featured

• ISDN line profiles, including SPIDs, switch type and LDNs, can be stored in nonvolatile memory for up to 10 different locations. (North American version only.)

• Last number dialed is automatically stored in memory.

• Up to 39 numbers can be stored in nonvolatile memory.

• Two audio inputs are provided: Mic/Line on a 3-pin XLR, plus a separate mini-jack input.

• Includes two audio outputs: 1/4" phone jack and line-level on XLR. The output is an externally controllable mix of local program audio and studio return.

• An internal peak limiter keeps the audio from clipping in case of a sudden increase in level — useful in those sports remotes.

• An ancillary data port allows you to connect a computer to the Nexus for a 4800 baud modem channel that runs at the same time as your audio — great for call screening.

• The Nexus includes a contact closure that closes when the "ready" light comes on.

• The Nexus is also available in a 2U rackmount version. The input and output may be fixed at 0 dbu. Rackmount and portable units are interchangeable.

Nexus is versatile

• For the occasions that you don’t have ISDN, the terminal adapter can be bypassed. There is a data port that can be used with switched 56 DSU/CSUs, DDS, fractional T1/E1, etc.

• For a point-to-point connection under 3 miles, the Nexus doesn’t even need ISDN! The Limited Distance Modem feature (LDM) allows the Nexus to deliver 15 kHz bidirectional audio on plain copper. (North American version only)

• STL Backup Mode lets the Nexus automatically dial a stored number when it receives a contact closure.

• External Command Mode lets a user dial the Nexus from a computer using AT commands.

About the Terminal Adapter

The Nexus contains both a terminal adapter (and NT1 in the North American version). It is designed to connect directly to the ISDN   interface provided by the telephone company.

The North American version Nexus supports the following switch types: National ISDN 1, AT&T 5ESS and Northern Telecom DMS-100. The Euro version of the Nexus supports the International S/T switch type: ETS1-Euro ISDN Standard.

The unit will work at 56, 64, 112 and 128 kb/s. To support 112/128 kb/s data transmission, the Nexus has a built-in Inverse Multiplexer (IMUX) that combines and synchronizes the two BRI ISDN "B" channels. It uses an IMUX protocol called BONDING.

Applications

The Nexus provides a cost saving alternative to satellite feeds or dedicated circuits. It is ideal for applications requiring high quality (7.5 or 15 kHz) mono audio. This codec is the best choice for remotes involving live programming such as talk, news, and sports, where real-time cueback is essential.

Also, since G.722 is an international telephony standard, the Nexus provides compatibility with a large established base of users worldwide including the DXR.1 and DXP.1 made by Comrex.

About the Algorithm

The G.722 algorithm is an international ITU standard which uses Adaptive Pulse Code Modulation (ADPCM) to achieve a 4:1 data reduction, allowing more audio information (or wider bandwidth) to be sent along a voice grade digital channel.

The Nexus incorporates 64X oversampled Sigma Delta A to D and D to A converters. The algorithm is run on a single ADSP-2181 DSP and uses a statistical synchronization technique which is continually updated by the decoder. When used in ancillary data mode, H.221 synchronization is used. Audio is sampled and reconstructed at 16 kHz (7.5 kHz mode) or 32 kHz (15 kHz mode) with 16 bit quantization. The Nexus automatically adapts to 56, 64, 112, or 128 kb/s.

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