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Frequently Asked Questions

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IP / BRIC | GSM | POTS | ISDN
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IP / BRIC

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GSM

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POTS

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ISDN

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Phone Systems

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Miscellaneous

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ACCESS

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Matrix

See also: GSM FAQs | POTS FAQs | ISDN FAQs | Misc FAQs

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BlueBox

See also: POTS FAQs | Misc FAQs

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Vector

See also: POTS FAQs | Misc FAQs

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Nexus

See also: ISDN FAQs | Misc FAQs

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Envoy

See also: ISDN FAQs | Misc FAQs

 

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STAC

See also: Phone System FAQs | Misc FAQs

 

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Q: Why should I care about audio over IP?

A: Because ISDN is going away fast and GSM is troublesome at best. Many radio stations and networks have relied on these technologies for remote broadcasts. The telephone company is making ISDN more difficult or impossible to get, and there are limited alternatives. For GSM, Cingular has made it difficult or impossible to get new data accounts to work with codecs, and T-mobile is showing signs of obsolescing the service as well. We are advising new GSM customers to proceed with caution.

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Q: What about POTS codecs?

A: We expect POTS codecs to become more popular as ISDN sunsets. But POTS codecs depend on modem connections, and as the telephone network changes to an IP-based system, we expect increasing troubles in making modem connections, especially long-distance.

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Q: OK, I’m worried. What’s the solution?

A: The future clearly points in the direction of Internet-based connections for remote broadcasts. Internet access is becoming easier to get than dial-tone and certainly has a better outlook than ISDN.

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Q: I see lots of companies talking about IP audio—What’s Comrex’s spin?

A: First, let’s define the scope of our solution—We’re the remote broadcast guys. Our solution is fundamentally different than systems like Axia (and others), who are concerned with Ethernet audio transfer within a facility, and Harris/Intraplex (and others) who are concerned with moving audio over managed LANs and WANs. These solutions assume you have control over the network at both ends (and in-between). Remote broadcasters don’t have that luxury. We need to work on the public Internet. Of course, because our system is “hardened” for the Internet means it will work even better on managed networks.

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Q: I’ve talked to folks who’ve tried this IP audio on the Internet thing, with mixed results. Is it “ready-for-prime-time”?

A: It’s pretty easy to build an IP audio codec that works well over an Ethernet cable. These systems will have their good and bad days on the public Internet. We’ve spent the last few years developing Comrex BRIC technology, which moves Internet audio closer to the ISDN experience. BRIC stands for Broadcast Reliable Internet Codec.

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Q: Can I get an executive summary of BRIC?

A: BRIC uses very small data streams, because the less network data you use the kinder the network is to you. It also is super-smart about how to cover up the failures of the Internet. Next, it automatically applies only the minimum delay needed to keep the connection stable. Finally, it makes the system easy to set-up and use, so you can give it to your remote kid and he can figure it out quickly. BRIC technology is an excellent choice for any application currently served by ISDN—Voiceover, Studio-to-Studio, backup STL, weather, sports and talk syndication, etc.

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Q: Are there any other advantages to this BRIC stuff?

A: Using BRIC codecs can be a liberating experience! Because Internet is now available in so many ways at so many places, you can leverage this to get truly mobile. Besides DSL and cable modem access, many retail outlets now provide Wi-Fi service, so you can use that for your broadcast. 3G cellular services are widely deployed that bring Internet virtually anywhere. New, low-cost satellite services are now available. We’ve literally run BRIC codecs from planes, trains and automobiles.

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Q: So do I just go buy a BRIC?

A: BRIC is the name of the underlying technology, kind of like Pentium is to a PC. We utilize BRIC in our products called ACCESS codecs and they are available in two packages (like all remote equipment should be): Rack mount (for the studio) and portable (for the road). Both move full-duplex, real-time mono or stereo audio over the Internet. An ACCESS codec is required at each end of the audio link, but Portables and Racks are interchangeable.

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Q: What’s the difference?

A: ACCESS Rack:
• Designed for in-studio use.
• No user controls, and you “drive” it from a web page served from the ACCESS using any web-browser.
• Line-level analog and digital audio ports, and connects only to an Ethernet network.

ACCESS Portable:
• Battery or AC Powered hand-held unit, about the size of a camcorder.
• PDA-style touch screen user.
• Single audio in/out, but can be “docked” with a clip-on mixer to provide a
six channel stereo system with six headphone ports.
• Built-in Ethernet.
• Laptop-style card slot for connection to other networks like dial-up, Wi-Fi,
and 3G cellular.

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Q: Are there any options to buy?

A: ACCESS is delivered ready to work on the Internet or POTS lines using a range of coding algorithms-- from stuff that will work on “barbed wire”, to uncompressed audio that requires a very fat network. One option available is a software upgrade to enable an additional four encoding algorithms, all based on the well regarded AAC (licensed by Fraunhofer IIS) family of audio compression tools*. We consider this our “audiophile” upgrade, since the AAC modes deliver audio preferable to “golden ears”, but generally require a better network than the default encoders. The upgrade provides AAC, AAC-LD, HE-AAC, and HE_AACv2. Another option is the “docking” mixer for the portable, when available.

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Q: What about all of my existing POTS codecs?

A: Both ACCESS Rack and Portable are POTS codecs too. They will talk to all your older Comrex codecs (excluding Hotline). So you can replace your Studio POTS codec with ACCESS rack, and take calls from either POTS or IP users. POTS codec mode has one added feature—when dialing between ACCESS, stereo audio is available on a single POTS line.

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Q: Will you be able to talk to other manufacturers IP codecs?

A: Comrex is working hard within the industry to establish compatible modes using the AAC-based encoders we provide as an option. When used with other manufacturers systems, some of the BRIC enhancements won’t be available. Standard BRIC encoders are proprietary to Comrex and will not likely be compatible with other codec offerings.

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I've always dreamed about using mobile phones for remotes. Has Comrex made my dreams come true?

Comrex has shared your dream, but for years the realities of available mobile networks and associated technologies would not support broadcast remotes with sufficient quality and reliability. When we originally released the Matrix Portable Codec in 2000, it was designed to accept a high-quality wireless interface, but we would not release a product until we could provide the quality you expect from us.

Advances in GSM, as well as the ingenuity of our development team, enable us to now offer a fully-integrated Matrix GSM Module for Matrix Portable for wireless remotes. The module includes a built-in GSM wireless phone, compatible with GSM carriers and capable of operation in most of the world.

Unfortunately, i n the US, T-Mobile and Cingular who once sold and supported the service required for GSM , recently have been discontinuing the Circuit Switched Data service without warning. It has become increasingly difficult to reliably obtain CSD service or to be able to rely on this service for broadcasts. And sadly, broadcasters don't have enough clout to motivate the phone company to continue offering this service.

The future of wireless remotes will be over IP using the ACCESS codec. Please see http://www.comrex.com/products/access.htm  for details.

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Why is using mobile phones more difficult than using landlines? After all, my Comrex POTS Codecs sound great.

Despite the developments in mobile technology, sending high-quality live audio over a wireless phone call is still a challenge. While there are several wireless phone technologies today, only one, GSM (Global System for Mobile Communications), has a data spec stable enough for audio codec use. As part of its standard, GSM offers a data service called Circuit-Switched Data (CSD). For the length of a call, CSD establishes a dedicated channel linking together all of the segments of the signal path, permitting constant data throughput. Without CSD, the data path would be too choppy for real-time audio, with fluctuating data rates and stalled packets.

Furthermore, GSM offers a very limited data rate - only 9.6 kbps, so we had a challenge to develop software to transfer good-sounding audio on such narrow bandwidth.

For more technical information on GSM, see our GSM Primer.

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How is GSM availability?

Outside North America, GSM has become the world standard for mobile phones.

In the U.S., companies including T-Mobile and Cingular have introduced service to most cities and suburban areas, and beyond. Both companies offer services suitable for live audio transmission.

However, recently they have been discontinuing the Circuit Switched Data service without warning. It has become increasingly difficult to reliably obtain CSD service or to be able to rely on this service for broadcasts.

Canada is covered by Rogers Wireless and Microcell Telecommunications, while TelCel covers much of Mexico. These GSM carriers, however, do not offer CSD at this time, so the GSM Module can only place voice calls in these countries.

These maps can help you determine GSM coverage in your area. Note that many maps err on the conservative side. For example, Comrex's headquarters in Massachusetts are shown in an area with weak coverage, but a strong signal is actually present.

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What is circuit-switched data? How do I order it?

Circuit-switched data (CSD) is a service that provides constant bandwidth (9600 baud, in the U.S., slightly higher elsewhere) from your GSM phone to a landline. This constant throughput is crucial for real-time audio broadcasts. Other protocols utilize packet-switched methods, which may provide higher speeds but transmit in bursts and pauses. Unfortunately, with this fluctuation in bandwidth, packet-switched connections cannot support real-time audio transfer.

GSM carriers around the world generally activate CSD as a standard part of GSM accounts. But due to its high demand on network bandwidth, some companies, mainly in North America, do not offer CSD.

In the US, while T-Mobile and Cingular once sold and supported CSD, recently they have been discontinuing the Circuit Switched Data service without warning. It has become increasingly difficult to reliably obtain CSD service or to be able to rely on this service for broadcasts.

CSD is not currently available on GSM networks in Mexico and Canada.

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What mobile phone do I use with the Matrix GSM Module?

The Matrix GSM Module actually has an embedded GSM phone, so no external phone is necessary. Simply insert the SIM card from your carrier to activate the phone and make calls.

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Do I need special equipment for international remotes?

You may. Previously Comrex produced the GSM Module in two versions. The North American version has recently been discontinued. This is due to the fact that in the US, while T-Mobile and Cingular once sold and supported CSD, recently they have been discontinuing the Circuit Switched Data service without warning. It has become increasingly difficult to reliably obtain CSD service or to be able to rely on this service for broadcasts.

The International version supports the 900 and 1800 MHz bands. Some countries utilize other bands, so be sure to check with the international carrier before ordering a module.

Also, while your SIM card will probably work with almost any GSM network on the planet, we recommend arranging a local SIM card to avoid pricy roaming charges.

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Can I place regular voice calls with Matrix Portable on GSM?

Yes, once this option is manually enabled. Power down the unit and reboot it with the GSM module removed. Then, enter the hidden menu by pressing HANG UP three times. Select "4" for MORE, and "5" for more. Choose "4" for GSMVoice, and select "1" for Enable. Press CANCEL until you are at the Main Status Display. Now, when you boot up, with the GSM module installed, the menu will include "Dial Voice", allowing you to use the Matrix as a mobile phone with convenient microphones and headsets, even if you do not have circuit-switched data available.

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The Matrix gets a great GSM signal rating, but all my calls say "NO CARRIER".

Your account is not set up properly for circuit-switched data. This is typically a problem with Cingular, and you should remind them that you need Wireless Internet. For more tips, see Circuit Switched Data.

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My studio Matrix answers a GSM call via its landline, but after negotiation, it does not successfully connect.

The studio unit needs to be set to expect a GSM call. The main display of your studio Matrix or BlueBox needs to say "GSM" in the top right corner; if not, press Enter, and choose Config, Codec, and select GSM (Pots Side).

If "GSM" is not listed, you may need a software upgrade. You can check this in the field by viewing your current firmware revision.

Remember to change the studio unit's Codec setting to Music or Voice before the next call from a POTS codec. On the Matrix Rack, you can control this setting via the Aux contact closure - see our tech note.

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What do I use to receive a GSM call in the studio - another mobile phone?

You can simply call into a Matrix Portable, Matrix Rackmount, or BlueBox on a landline in the studio. Any of these units can be used but it may require a complimentary upgrade. For more information, contact Comrex Tech Support with your unit's serial number, or check your unit's current software for compatibility.

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How do I see if my Matrix/BlueBox is compatible to receive GSM calls?

To determine your current software, navigate to the main menu and press HANG UP three times to enter the hidden menu and choose REV. GSM operation requires Module 7.0 or higher; and Matrix Control software 8.0 or higher or BlueBox Control software 2.0 or higher. Control software can be downloaded online. If you have an earlier Matrix revision, contact Tech Support for more information.

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How is the wireless sound quality?

We've made every effort to have it as good as possible. A new Comrex coding algorithm gives you frequency response of up to 7 kHz with reduced digital artifacts. New error correction and modem technology mean better stability for your connection.

However, you have a mobile telephone call and coded audio, both subject to situational variables. Field reviews have ranged from "satisfactory" to "I can't believe it sounds this good!"

Quality is subjective, so you should judge it for yourself for deciding. To hear clips, visit our audio page or contact us for a free demo CD.

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Can I call from the studio to a Matrix on GSM?

Maybe. The Matrix is able to answer a wireless data call, but this feature's availability varies by provider and market.

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Can I connect from the field on a regular landline, if I accidentally leave the studio codec set for GSM?

Yes. For best results, we recommend resetting the codec in the studio unit to expect a POTS call, but in a pinch, you can set the field Matrix Portable for SMR (Save My Remote) mode. If the module is installed, turn off the power, remove the GSM Module, and reboot. Press Enter from the main screen, and choose CONFIG, CODEC, and GSM (POTS SIDE). While this has limitations (you need to connect at 14kb/s or higher; renegotiations are disabled; and the effective data rate is one speed lower than the actual modem connect rate), this will help save your remote.

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Does the future bode well for real-time audio data?

Wireless is moving toward the so-called 3G, the third generation of wireless technology, following analog (1G) and PCS (2G). 3G promises rates from 384 kbps to 2 Mbps in a stationary environment, supporting wide-bandwidth needs such as full-motion video. While the bandwidth will remain Internet protocol-based and subject to congestion, design for multimedia and wide bandwidth will help reduce today's limitations.

Early 3G networks have already begun to spring up. In Japan, NTT DoCoMo launched its 3G "FOMA" service in October 2001, and European networks are in development. Implementation in North America should be introduced in the upcoming years.

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How do I dial the integrated phone?

All dialing functions are conveniently controlled via the Matrix keypad.

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How do I know my signal strength?

The Matrix Portable displays the wireless strength signal, on a scale from 0 to 32. We recommend a reading of at least 20.

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Can the Matrix GSM Module improve my reception?

Yes. The module kit includes a three-inch external magnet-mount antenna for optimal reception. Also, since the phone is not handheld, it is not limited by radiation concerns and can safely transmit more power than traditional handheld phones.

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Where should I place the antenna?

As high as possible. If you have trouble, try reorienting the antenna. Sometimes placement in the immediate area will change reception dramatically. Whenever possible, attach it to a steel surface, like a car body or even a pie pan, for a ground plane.

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Can I do a wireless remote with any of the other Comrex POTS codecs?

The optional GSM wireless module for Matrix Portable is an integrated solution and the only solution providing a frequency response of up to 7 kHz with reduced artifacts. But Matrix Portable, BlueBox, and Vector can be connected to the hands-free port of many mobile phones. Although audio quality is not much better than a standard mobile phone call, it provides a useful backup tool. Microphones and headphones may be interfaced with the "hands-free port" on a variety of cell phones by using the optional TelCell module on the Matrix Portable or the "Cell Phone Jack" on the BlueBox. While this method is limited to the phone's frequency response, professional microphones will typically lead to an audible improvement over the cheap ones found in most mobile phones. For detailed information, see Comrex Tech Note 229.

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I have heard a lot about wireless Internet using GPRS. Is this compatible with Comrex's GSM solutions?

GPRS (General Packet Radio Service) is one of several interim ("2.5G") solutions using the public Internet for data transfer. GPRS is good for web browsing, e-mail and portable multimedia. But packet-based data, sent through the Internet, is in danger of network congestion and delays, which are clearly not good for real-time broadcast.

We are not supporting codecs on these so called "2.5G " services for several reasons:

1. Data throughput is typically asymmetrical on these services. They transmit high speed from the network to the wireless phone, but allow only low speed transmission from the wireless phone to the network. The path from the phone is the direction we need the greater throughput.

2. Rather than dial-up services, these are connections via the public Internet. Similar to the services from your ISP, they are subject to the congestion and unpredictability associated with Internet delivered data.

3.These services are "best effort," meaning that if someone makes a voice call within your cell site, your data rate can be throttled down.

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Will the Matrix work on HSCSD? How about European 14.4 GSM?

High Speed Circuit Switched Data (HSCSD), implemented by some European wireless providers, uses two telephone channels for up to a 28.8 kbps data rate over GSM with audio frequency response as high as 10-12 kHz. The problem with HSCSD is its "best effort" implementation, which means that, when demand on the GSM system is increased, the carrier can remove the high-speed data by dropping one of the two channels whenever it chooses to, without notifying you. This results in the interruption of audio. The uncertainty of the HSCSD connections in real world situations makes it difficult, if not impossible, to use for live broadcast.

An "enhanced" GSM data service delivering a data rate of up to 14.4 kbps on a single wireless channel is also available in the UK and other places in Europe. The Matrix Portable is being used successfully on this service, delivering higher quality audio than can be achieved on the more limited 9.6 kbps GSM available to most users. This 14.4 kbps service tends to be far more robust than the HSCSD dual channel implementation.

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What is a POTS Codec?

POTS is an acronym for Plain Old Telephone Service, the familiar dialup telephone service that we use every day. (In some parts of the world, this is also called PSTN, Public Switched Telephone Network.)

A codec is a coder-decoder. A signal goes into the "coder" part and is processed according to a given function. In this case, analog audio is converted to digital and then processed (digitally compressed) to reduce the size of the digital signal. On the "decoder" side, the opposite happens: the signal goes through digital decompression and then is converted back to analog audio.

Functionally, POTS Codecs are used in pairs. At one location, a POTS Codec is used as a coder, sending the compressed digital signal to the other location via the POTS line where the second POTS Codec decodes the signal. Comrex POTS Codecs are fully bidirectional, allowing both units in the pair to transmit and receive high-quality audio.

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When would I want to use a POTS Codec?

POTS Codecs are most commonly used for live broadcast of news, interviews, traveling talk shows, sports, and entertainment audio. POTS Codecs often stand by as backups when ISDN or satellite is used for a primary feed. Some radio stations use a POTS Codec as a backup to their studio-to-transmitter link.

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How do POTS codecs compare to ISDN?

POTS codecs are ideal for grab-it-and-go situations. When quality is paramount, however, ISDN is the clear choice. Here is a quick summary:

  • SETUP: Faster with POTS.
  • USABILITY: Easier with POTS.
  • AVAILABILITY: Better with POTS.
  • INSTALLATION TIME: Shorter with POTS.
  • COSTS: Lower with POTS.
  • AUDIO QUALITY: Best with ISDN.
  • LINE STABILITY: More predictable with ISDN.

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How do POTS Codecs sound on the air?

Comrex has elevated POTS Codec performance to a new level, providing low-artifact, two-way 15 kHz audio response on most connections. When telephone line quality is below standard and does not support full data rates, our POTS Codecs can adapt and provide lower audio response rather than drop the connection. As computer modem users know, connection speeds are not as good on some phone lines as they are as on others. The same is true with POTS Codecs. We specify up to 15 kHz audio performance on typical phone lines that are able to function at data rates of 24 kbps and above. On lines with data rates as low as 9.6 kbps, your Comrex POTS Codec will provide acceptable audio quality for broadcast:

Audio Frequency Response

Data Rate (kb/s) Matrix/Vector Mode Hotline Mode
9.6 ........................ 5 kHz ................ n/a
12 ......................... 6 kHz ................ 4.5 kHz
14.4 ...................... 7 kHz ................ 5.4 kHz
16.8 ...................... 7 kHz ................ 5.6 kHz
19.2 ...................... 11 kHz .............. 5.8 kHz
21.6 ...................... 12 kHz .............. 6.5 kHz
24 ......................... 15 kHz .............. 7 kHz
26.4 ...................... 15 kHz .............. 8 kHz
28.8 ...................... 15 kHz .............. 8.6 kHz
31.2 ...................... 15 kHz .............. 9.3 kHz
33.6 ...................... 15 kHz .............. 10 kHz
Coding Delay 100 ms 120 ms

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Can the POTS Codecs both send and receive audio?

Yes, all Comrex POTS Codecs can send and receive audio simultaneously, so program and cueback can be sent over the same phone line. This is a real advantage when off-air monitoring is delayed from real-time, such as with HD Radio, when using a profanity delay, or where off-air monitoring cannot be used on live remotes.

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I've seen some devices by Comrex that are called "frequency extenders". Are these POTS Codecs? No, they are not. Frequency extension is an early technology, developed by Comrex and introduced in 1976, to improve the quality of audio transmission over POTS lines. While many of the thousands of frequency extenders remain deployed, our introduction of the ?rst high-quality, dependable POTS Codecs in 1996 again redefined remote audio transmission over POTS. For more information on frequency extenders, visit the LXT/R product page.

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1996 was a long time ago in technology years. Have you kept up?

Absolutely. While our first POTS Codec (HotLine, affectionately called the "Red Box") is no longer manufactured, we still support and provide occasional software updates to keep HotLines, and all of our POTS Codecs, as up-to-date as possible.

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What POTS Codec models do you offer now?

We offer three choices for use in the field: Matrix Portable, BlueBox, and Vector elevate POTS performance to new levels, providing up to 15 kHz audio response on most connections. They are designed to be very portable, used virtually anywhere in the world, and operated by non-technical staff. For the studio side, the Matrix Rack is the perfect companion to all of your field POTS Codecs. Every Comrex POTS Codec is compatible with the others, including the original HotLine.

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Mobile phones are almost POTS. Do these POTS Codecs function wirelessly using the mobile phone network?

Yes. All three portable units can be connected to the hands-free port of many mobile phones. Although audio quality is not much better than a standard mobile phone call, it provides a useful backup tool.

Plus, there is now an optional GSM wireless module for Matrix Portable that incorporates mobile telephone technology with a new Comrex audio coding algorithm. Frequency response of up to 7 kHz is possible with reduced artifacts. Comrex is the first to introduce this new option in remote broadcast, and the reviews from the field are excellent.

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How do I know which Comrex POTS Codec is best for me?

All of our POTS Codecs offer a core feature/function set that includes the standard-setting Comrex audio quality and reliability. Choice of a field unit depends primarily on your input, output, and mixer requirements.

  • Matrix Portable offers the greatest flexibility, as optional modules allow it to be used with ISDN and GSM wireless in addition to POTS.
  • BlueBox, with a single input and single output, is your best choice if you have a tight budget or need the smallest POTS Codec with no compromise in performance.
  • Vector incorporates a full-featured remote studio in a three-pound package. Non-technical users appreciate its easy-to-use interface.

For the studio, Matrix Rack works with all of our POTS, ISDN, and GSM Codecs, as well as those from nearly everyone else. Matrix Rack provides a great home base for every remote you may do.

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Don't other companies make POTS Codecs? Why should I buy Comrex?

Confidence is the best reason. When you purchase any Comrex product, you can be confident that you are using the most rugged and reliable remote broadcast equipment available. We've been at this for 40 years and understand that with live broadcast, you don't get a second chance. Ease-of-use and reliability save you time and money on training and downtime. Problems with our POTS Codecs are rare, but when they do happen, our support is fast and effective. That's why there are more Comrex POTS Codecs in the field than all other brands combined. If you are still not convinced, contact Comrex or your favorite broadcast dealer for information on a no-obligation demo.

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So if I put a Comrex Codec side-by-side with the other guy's unit, the Comrex will perform at least as well and probably better?

You don't expect us to be modest, do you? But our reputation demands that we be honest. The answer to your question is "Yes" if you compare POTS Codecs carefully.

  • Performance of all POTS Codecs is dependent on telephone line quality that can vary from call to call, even on the same line. So side-by-side comparisons can be anecdotal rather than scientific.
  • As previously noted, our original HotLine was introduced some time ago and there are many thousands of these units deployed. When comparing HotLine with Comrex's current POTS Codecs (or those from other manufacturers), these newer products will, of course, perform better. We offer our HotLine customers special programs to help them trade-up their "Red Box" to our latest technology.
  • This technology advances quickly. Comrex provides our POTS Codec customers with free performance updates. Without these updates, our users may not be getting the best from their units.

We are confident that, in comparison tests using our current range of products, Comrex POTS Codecs function as well, if not better, than anything on the market.

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I am buying a Comrex Matrix and BlueBox. Will they work OK with my HotLines and Vectors?

Ahh. a steady customer! The Codec Answer Guy well knows the connection between folks like you and his paychecks! The Matrix will automatically realize that it is talking with a HotLine or Vector and will switch to the appropriate mode. Unless your Vector or HotLine has been upgraded in the last few years, you should contact us about an upgrade that will insure maximum happiness with the newer modem in the Matrix. Also, you may want to turn off the Error Correction feature on the HotLine, particularly when used with the Vector.

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When I make a credit card call with my Matrix, how do I make it pause to wait for the "bong" or the message that tells me to enter the rest of the numbers?

Easy one. While entering the numbers, just use the QDIAL key to insert two-second pauses. You'll see a comma on the screen for each of them. Same goes for the HotLine and Bluebox. With the Vector, use the "Insert Pause" key next to the screen.

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When I have a remote at a location with a digital phone system, can I plug my codec right into the jack at the broadcast location?

You can, as long as you avoid digital PBXs. There are two ways to confirm that you have a plain analog phone line. The high-tech solution is to get an IBM Modem Saver, Konexx ModemMinder, or similar test gadget to test the line first. The low-tech approach is to bring a cheap "plain old phone" along, and see if it works. If you get normal-sounding dialtone and can place calls, you should be all set. If your plain phone gets damaged by a digital PBX, it's a good warning sign not to plug in your codec.

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Can I share the studio codec's telephone line with a fax machine?

While it may function properly, for best results, we highly recommend that nothing else is connected to the same line as the codec. Also, make sure that your inside wiring is done with good twisted pair phone cable - Category 5 or higher computer network cable is great. If you must share a line with other equipment, try to actually disconnect the other stuff when you are using POTS codecs.

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Our station will be doing three days of remotes in Outer Snorovia. Will our POTS codec work from there?

Here are some tips to maximize your remote success. First, try to get a direct outside line, if possible. If you must use a hotel phone system, ask questions about how well modems work on those lines. Second, check your manual for Country Code settings. If there isn't a specific one for that country, try the North American version first, and then experiment if you have trouble getting dial tone or receiving calls. (If all else fails, you can dial manually by connecting an external phone to the codec.) Third, realize that the greatest problems may be in calling in or out of the country. If Outer Snorovia is connected to the rest of the world by fiber-optic cable, you will probably do very well. Satellite, old microwave links or old undersea cable will give the greatest troubles. Be prepared to try different long distance companies, and dialing in both directions. Fourth, the Codec Answer Guy reminds you that they call it "Snorovia" because of sounds made by their sleepy telephone workers.

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How do I improve my connect speeds? What does it mean if only one ready light comes on?

For improved connect speeds, you can first gauge the performance of each codec and the network between them. To isolate these factors, try the following steps:

  1. If either unit is a Hotline, disable Error Correction by pressing Enter, choosing (3) Config, (3) More, (2) ErrCorr, and (2) Error Correction Off. When you return to the main screen, the letters EC should not be present.
  2. Call from each unit into the Comrex test line (978-784-1700) and listen for a few minutes. If you cannot get a good connect speed, you might try trying two or three times. Note these connect speeds, and the Ready light status. (When you call Tech Support, we will generally start by having you connect with the test line, so please call ahead at your convenience.)
  3. Flush, or reset, the modem in both units. To do this on a Matrix or BlueBox, press the HANG UP key three times from the main status display, and choose FLUSH MODEM from the menu. On a Vector, reboot the unit, and when you see "INITIALIZING." in the display, press the bottom soft-key to the right of the display. For a Hotline, when you reboot the unit and see "SELF-TEST", press the CANCEL key.
  4. Call from one codec to the other, and see if the connection speeds have improved. If not, try step 2 again and see if the results have improved.
  5. If the problem persists, especially on one codec in particular, test the codec(s) on other phone lines, or even in other buildings.
  6. See Tech Note 202 for hints on improving modem connections.
  7. If none of these help, contact Comrex Tech Support for more information. If your codec has minor damage, it may still function but with reduced performance, so the unit may be due for repair.

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Are 33.6 kb/s modem connections the best?

No, usually. High speeds do not necessarily make a better broadcast. Your goal should be to achieve the highest speed at which the modem operation will be stable. Since slower connect rates are more tolerant of errors, some judgement is required to hit the right spot. In fact, the Answer Guy is partial to speeds of 28.8 kb/s and lower, as all V.34+ modems seem to be more stable at those rates. In addition, at any speed 24.0 kb/s or higher, the current POTS codecs (Vector, BlueBox, and Matrix) level off at 15 kHz, so faster speeds are not necessary. Use the MaxRate to set a ceiling that works in your area.

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How can I get a compatible codec for my Hotline?

The HotLine will connect with any other Comrex POTS Codec, in Hotline mode. For best results, make sure you have the latest firmware upgrades, and disable error correction. If you have questions, contact Tech Support.

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Any tips for baseball games and other long broadcasts?

Bring a snack! And during hours-long broadcasts, the Codec Answer Guy humbly suggests that you consider shorter phone calls. The modem in your Vector (Matrix, HotLine) works by negotiating settings based on all kinds of electrical characteristics of the phone circuits through which your call is routed. After a couple of hours of use, those figures may change, and you might do yourself a favor by redialing the call during a break in programming. This isn't a hard-and-fast rule; just a suggestion that may save you some troubles.

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How can I create the most reliable contact closures?

Line noise can lead to false contact closures, so we recommend two options. First, if you build a circuit at the studio to reject all closures shorter than, say, one second, you simply have to press the closure key for one second or more. This way, false contact closures will not cause problems.

Alternatively, for multiple independent contact closures, you can use the Matrix's serial data connections to send and receive dependable contact closures. We recommend the Broadcast Tools SRC-8 III for such use.

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How do I improve my Vector/Hotline power connection? After 7 years on the road, it's gotten flaky.

If the power jack on your HotLine has the letters "SWC" visible from the back of the unit, we would like to see it replaced. Otherwise, or if you own a Vector, a little cleaning usually cures any intermittent operation. The most durable cleaning process is a two step operation. First, squirt a little solvent-type cleaner (such as Caig Labs CaiKleen 41 or Chemtronics Electro-Wash PX) into the power plug. Then insert the plug into the jack on the codec, and rotate the plug to wipe the contacts. Now remove the plug and squirt some Caig Labs DeoxIT into the plug, and repeat the wiping process. The DeoxIT coating will last quite a while, so you shouldn't have to do this very often.

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How do I dial with an external phone?

We recommend that you get the codec ready before dialing by bringing up the screen instructing you to dial with an external phone. Dial the call on the phone, and as soon as you hear the first ring, press enter on the codec and hang up the phone right away. Don't wait until the modem at the other end answers, or the off-hook phone will become part of the negotiation. Also, please note that the Matrix and BlueBox can take a 44 digit dialing string without the need of an external phone, and with current software, the Vectors and HotLines can also accommodate the extended string. If you have an older Vector or HotLine that won't do this, contact us for the free firmware upgrade.

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My codec sticks on "Initializing" and will not completely boot up.

If you have a Vector, make sure that none of the buttons are sticking behind the screen. If this does not help, or if you have a BlueBox, Matrix, or Hotline, please contact Comrex Tech Support . If you have a Matrix, please note the number of dots on the "Initializing" screen.

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What is an ISDN Codec?

ISDN is a digital dial-up telephone network, which can be configured for data as well as voice telephone service.

A codec is a coder-decoder. A signal goes into the "coder" part and is processed according to a given function. In this case, analog audio is converted to digital and then processed (digitally compressed) to reduce the size of the digital signal. On the "decoder" side, the opposite happens: the signal goes through digital decompression and then is converted back to analog audio.

Functionally, ISDN Codecs are used in pairs. At one location, an ISDN Codec is used as a coder, sending the compressed digital signal to the other location via the ISDN line where the second ISDN Codec decodes the signal. Comrex ISDN Codecs are fully bidirectional, allowing both units in the pair to transmit and receive high-quality audio. Also, Comrex ISDN Codecs utilize industry standards, so they can communicate with many other manufacturers' ISDN Codecs around the world.

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When would I want to use an ISDN Codec?

ISDN Codecs are most commonly used for remote broadcasts of traveling talk shows, traffic and weather services, and sportscasts. Today, many on-air personalities have ISDN connections at their home in order to broadcast from a home studio. Some radio stations use an ISDN Codec as a backup to their studio-to-transmitter link.

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How do ISDN codecs compare to POTS?

ISDN delivers the highest quality audio, with the low delay necessary for fast-paced exchange. POTS, on the other hand, are perfect for spontaneous broadcasts. Here is a quick summary of each technology's advantages:

  • AUDIO QUALITY: Best with ISDN.
  • LINE STABILITY: More predictable with ISDN.
  • EQUIPMENT COSTS: Lower with ISDN.
  • SETUP: Faster with POTS.
  • USABILITY: Easier with POTS.
  • AVAILABILITY: Better with POTS.
  • INSTALLATION TIME: Shorter with POTS.
  • COSTS: Lower with POTS.

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How do ISDN Codecs sound on the air?

Comrex ISDN Codecs utilize proven industry standards for high-quality digital audio, so most listeners will never guess that your talent is out of the studio! All Comrex ISDN Codecs use G.722, an international standard delivering 7.5 kHz audio with an imperceptible 6ms delay, as well as "Turbo G.722" for use with other Comrex ISDN codecs, which sends 15 kHz audio with the same low delay. (The Matrix also features MPEG Layer III to send and receive 15 kHz audio at 64 kb/s.)

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Can the ISDN Codecs both send and receive audio?

Yes, all Comrex ISDN Codecs can send and receive audio simultaneously, so program and cueback can be sent over the same phone line. This is a real advantage when off-air monitoring is delayed from real-time, such as with HD Radio, when using a profanity delay, or where off-air monitoring cannot be used on live remotes.

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What is a "U" Interface? What does this mean?

An ISDN circuit goes through several stages from the central office before it reaches your ISDN Codec. The important one for North America is the two-wire "U" interface, which connects directly to Comrex ISDN codecs. In contrast, ISDN connections on most other continents are supplied with the eight-wire "S/T" interface.

All Comrex ISDN Codecs are available for "U" interface, and the Matrix ISDN Module is user-configurable for either a "U" or "S/T" interface.

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Stations have no trouble calling me, but when I dial them, across the country, it says "Disconnecting".

This is probably a long distance problem. When you order ISDN service, unlike regular phone lines, you need to manually activate long distance service. If you have already signed up for a company, they might not have you set up correctly. We suggest going with one of the major companies for ISDN, as you stand a better chance of always getting your call through. If you are signed up already, call their data support numbers: AT&T (800-367-7956), MCI (800-283-6272), or Sprint (800-546-3282). If you use Fred's Long Distance, be aware that Fred has ISDN tin cans but is still using analog string.

You can also test your current long distance by forcing a call through a different carrier with a 7-digit PIC code. To do this, dial (10-10-xxx-1), plus the area code and number. Replace the XXX with one of the following codes: 222 (MCI), 288 (AT&T), or 333 (Sprint). Even if one fails, be sure to test all three carriers.

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The phone company just changed our area code. Do I have to re-program the SPID numbers in my Nexus or Envoy?

If your ISDN SPID numbers contain the area code (most do), you will probably eventually have to change them. The telephone companies usually allow a grace period during which either area code will work. Just remember to do it, or some day the power will go out, and the Nexus or Envoy won't be able to link up with the phone company switch. If you can update the area codes in your SPIDs and still get "OK" on the main screen, stick with the new settings. And please unplug the ISDN line before you change the SPIDs. You may get an error message otherwise. It's in the manual. Sorry. The Codec Answer Guy just couldn't resist saying that.

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What does "LNK C" mean on my Nexus display?

When you start up an ISDN connection, the Nexus will initially show "LNK DN" until it has its first conversation with the phone company switching equipment. You should then see a series of other "LNK" messages, ending with "OK." If the Nexus sticks on "LNK DN," something is wrong with the line or your connection to it. Sticking on "LNK B" or "LNK C" means that the first SPID number is not being registered. Similarly, "LNK E" or "LNK F" indicate a problem with the second SPID. The SPIDs have to match exactly with the numbers programmed in the telephone switch. These intermediate "LNK" messages usually mean that you've made a typo or that the phone company has given you the wrong numbers.

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SPID numbers give me a headache. Do you have a cure?

Yes, take two SPIDs and call me in the morning. (Sorry...) Actually, the SPID situation for North America is getting simpler. A few years ago, the telephone company people got together and established a simple SPID format for use on phone switches that use the National ISDN (1 or 2) software. That format is: AAA XXX XXXX 0101, where the "AAA" is the area code, and "XXX XXXX" is the local dialing number. In most cases, you will have two local dialing numbers for each ISDN line. If you are having trouble getting the "OK" on your Nexus or Envoy, you might want to try that SPID format along with the NI-1 switch type. Also, if you plan to use 112 or 128 kb/s data rates, you should enter the local dialing numbers (LDNs). While we will still continue to provide the older SPID information in our manuals, be advised that most of the new installations will have numbers ending in "0101".

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When I reprogram the SPIDs on my Nexus, I sometimes get a strange error message, like 'SS62'.

Be sure to disconnect the ISDN line when reprogramming your network settings (SPIDs, LDNs or Switch Type). Otherwise, you will likely get an error.

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After years, my Nexus/Envoy power connector has gotten flaky. Should I replace it?

If the barrel-style power jack on your Nexus has the letters "SWC" visible from the back of the unit, we would like to see it replaced. Otherwise (or if you own a Envoy), a little cleaning usually cures intermittent operation. The most durable cleaning process is a two step operation. First, squirt a little solvent-type cleaner (such as Caig Labs CaiKleen 41 or Chemtronics Electro-Wash PX) into the power plug. Then insert the plug into the jack on the codec, and rotate the plug to wipe the contacts. Now remove the plug and squirt some Caig Labs DeoxIT into the plug, and repeat the wiping process. The DeoxIT coating will last quite a while, so you shouldn't have to do this very often.

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How do I use a calling card on ISDN?

Unfortunately, since ISDN relies on digital connections, there is no way to hear conventional voice prompts to enter a calling card number, so we are unaware of a way to utilize calling cards. If you regularly broadcast from another party's ISDN line, you might force all your calls to a separate carrier using a PIC code (10-10-xxx), and set up third-party billing for that long-distance account. (Be aware that long distance companies charge high rates for manually-forced calls.) If you discover a way to use an ISDN calling card, please contact the Codec Answer Guy.

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How can I transmit contact closures using the Nexus or Envoy?

By connecting an external device or computer, your codecs can pass contact closures as RS-232 data. We recommend using the Broadcast Tools SRC-8 III for this purpose. Simply activate Ancillary Data on each codec for this to function properly. Note that this will only work when connecting to other Comrex codecs.

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Why won't my hybrid/coupler automatically disconnect?

The equipment watches for loop current to drop. Some PBXs, and even some telephone companies do not provide a sufficient loop-drop to be recognized.

To test the equipment for proper operation, simply unplug the telephone line. If the unit is working correctly, the unit will indicate that the call has been dropped.

Some companies' loop-drops are too brief to be recognized by the equipment. In this case, your phone company or PBX manufacturer may be able to help you.

If the problem persists, contact Comrex Tech Support.

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How many callers will STAC conference at one time?

STAC will conference a total of four callers (two on each hybrid). For best results, we recommend placing only one caller on each hybrid, for a total of two callers.

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If I have a 12-line STAC, can I use some control surfaces without sidecars?

Yes, but you won't be able to access the upper bank of lines

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What type of Internet server do I need for STAC IP?

STAC IP is integrated into the STAC mainframe, so no special hardware is necessary. To operate it locally, you can simply plug a monitor, keyboard, and mouse into STAC. STAC will also function as its own server, if you wish to have remote access throughout your facility, or anywhere else in the world. Just connect STAC to a live network connection.

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I only need 6 lines now, but can I upgrade my STAC later?

Sure! The expansion kit comes with the telco boards for your mainframe, a sidecar for your control surfaces to access lines 7-12, plus all the cables you need. (Sidecars are also available separately for additional control surfaces.)

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How many control surfaces can I use with STAC?

STAC will accommodate up to four physical control surfaces, plus a virtually unlimited number of users via STAC IP.

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Can STAC signal an external bell and light for ringing lines?

Yes. New units signal ringing lines at a contact closure on the mainframe. Early production units from 2004 may need an upgrade.

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Can I "tak" to callers using STAC IP?

No. If you use STAC IP for caller management, the control surface is necessary in order to speak with callers during screening. By associating a STAC IP session with a specific control surface, you can select lines onscreen, and route the call to the surface's handset, whether or not the surface has a sidecar.

And if you connect a headset to the control surface, you can hide the surface itself and handle all line selection from the STAC IP screen.

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How can I find out about upgrades for my Comrex unit?

Ask us! The key information we need is the model name and serial number of your Comrex equipment. While we certainly can help you over the phone, the Codec Answer Guy would appreciate your e-mailing (techies@comrex.com) or faxing (978-784-1717) the model names and serial numbers to us, along with your phone number. We can then look up the repair and upgrade information on those specific units, and call you back. This will save you some time on the phone, and guarantee the most complete answer. Some of the upgrades are essential for optimal product performance. Others may not even apply to the way you use the product.

Please be advised that we do not have any upgrades that cure bad phone lines. We do have some suggestions about how to deal with them. Take a look at Tech Tip 202 (Modem Line Checklist). Most upgrades for current products are complimentary.

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We have a lot of older Comrex stuff that came from a station we just bought. How can I find out if it works, and what I can use it for?

They should have clauses in radio station purchase and sales agreements that require manuals to be provided for all equipment! Anyway, Comrex has manuals and advice for all of our stuff, right back to the dawn of time (1961, by our reckoning). Just call us and ask for Tech Support. We can get you started. And if the gear was sitting on a shelf because it didn't work, we can see if we can fix it. Unless parts are no longer available, we should be able to help.

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How do I get an RMA number for repair?

Comrex does not actually issue RMA numbers. Please make sure, however, that you complete the repair form and include it with your equipment. And please explain your problems with as much information as possible - the more information we have, the faster we can find your problem. You can find all the repair forms on our Repair Page.

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The codecs sound great, but I'm told I need a mix-minus to get rid of echoes at the remote site. What is that?

The concept is simple. Don't send the audio from the remote back to the remote. Give them everything else they need to hear but not their own audio. This means that the "cure" is at the studio end, not at the remote. See Tech Tip 220 for more information.

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I lost my manual - how can I get a new one?

Manuals for all current Comrex products, plus many classic ones, are online. Please refer to our manual page . If you need a product manual that is not online, please contact Tech Support for more information.

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Tech Support


If you still have a question, please contact Comrex Tech Support. Phones are open from 8 AM - 5 PM EST.
978-784-1776
800-237-1776 (Toll-free in North America)
techies@comrex.com