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Matrix Hits the Streets Running

The art of sending high-quality audio over dial-up phone lines is difficult at best. I was told that the Comrex Matrix should reduce some of that difficulty.

The Motor Sports Radio Network Takes the Comrex Product for a Few Laps

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The art of sending high-quality audio over dial-up phone lines is difficult at best. I was told that the Comrex Matrix should reduce some of that difficulty.

The unit is a POTS codec. That means the send unit will digitize audio so it can ride over conventional telephone lines via a modem, and the receive end will convert the digitized data stream back into audio.

If this explanation sounds familiar, it should – this is how the company’s HotLine and Vector work as well.

Comrex equipped it with a DB-25 port where you can insert a module for an ISDN installation (G.722, G.722 Turbo and ISO/MPEG Layer III) or for a GSM cell phone. The ISDN modules are due out this spring and the GSM module will roll out later in 2001.

Right now, the Matrix is compatible with the Vector and HotLine, and if all else fails it can be used as just a POTS codec.
Product CapsuleThumbs up:

Versatile, solving remote problems with POTS and ISDN

Backward-compatible with Vector and HotLine

Store and Forward timeshifts audio file delivery

Straightforward manual

Easy and reliable mixing functions

Thumbs down:

Store and Forward audio more suited for voice recordings

ISDN and GSM modules not available yet

For more information contact Comrex Corp. in Massachusetts at (978) 263-1800, fax (978) 635-0401 or visit the Web site at
In the trenches

But Matrix is designed to be an all-in-one unit, with more than just codec features.

The field unit includes a two-input mixer, an additional input for a fixed-level mini-plug input (MD, cassette, etc.), headphone output and a balanced line-level output. The studio unit does not include the mixer or an interface for the cell phone, but does all the other features.

The unit has an optional Ni-MH battery, providing seven hours of primary power or hot backup when the AC adapter is connected. Both units have mini-jack connections for relays. These connections can be used to trigger a switch to operate automated features – a recorder or a tally signal for the board-op.

A feature called Store and Forward may save hassles in a control room or operations center. This can record 9 minutes 45 seconds of 15 kHz audio and upload it in a manner similar to e-mail. Both the send and receive ends of the Matrix are user-configurable to accomplish the appropriate store/forward function.

This feature is useful when producing drop-ins over a connection of dubious quality. The store-forward idea is good for busy newsroom operations.

A report could be recorded and uploaded to the studio where the operator could download or play the audio file. The file will stay in memory until it is erased deliberately.

In practice, the audio quality is more mid-fi than hi-fi, and music might not be appropriate over this part of the system. And the feature will only work with a properly configured unit.

The Matrix will pass 14 kHz audio with a connect rate as low as 24 kbps on a line in Music Mode. We made test calls to the Comrex Matrix dial-up test nodes in Massachusetts and in Great Britain. Even from our line that is five miles from the central Verizon office, the unit connected solidly at 24 kbps on both occasions.

In Voice Mode, the Matrix will pass 7 kHz bi-directional audio at speeds as low as 14.4 kbps, with a 300 bps data channel that might be appropriate for text messages.

Additionally, the Matrix will back up an STL. Should your studio link take a powder at the wrong time, go to the hidden menu and configure your studio end. It will dial a number at the transmitter site, where you have conveniently connected your similarly configured portable Matrix.

Wireless applications

Analog and first-generation digital cell phones do not support the Matrix technology yet. The reason is the systems cannot support the steady data rate needed for a codec to work and send quality audio.

The GSM technology is the best available, but still won’t equal that of a dialed-up POTS line. When the GSM module is released, the Matrix will pass audio at about a 5 kHz audio response rate. This rate may be acceptable for quick voice applications like drop-ins and news wraps, but not full-fledged remotes.

Tom Hartnett, vice president of engineering, and his crew get a gold star for trying to accomplish this, which is much like trying to stuff 10 pounds of sugar in a five-pound bag. Tom’s pamphlet “Wireless PCS Remotes: How and When” was so clear that even a non-technical person could understand why remotes can or can’t happen.

Comrex has always been noted for its straightforward operations manuals; this is as good a manual as I have seen for any piece of equipment.

Both the portable and studio versions cost $3,700. The battery kit is $450. The ISDN and GSM cell modules will sell for $850 and $500, respectively.

If there is such a thing as a serious one-size-fits-all remote solution, it is the Matrix. The unit can pay for itself simply because it has ability to back up an STL.

In addition, after three or four months of live client remotes several times per week at $800 a pop, the cost easily will be recouped.