Beyond ISDN: Welcome to the Age of the IP Codec | TALKERS magazine - talk media trade : TALKERS magazine

Beyond ISDN: Welcome to the Age
of the IP Codec

| February 25, 2013

By Thomas R. Ray, III CPBE, AMD, DRB
Tom Ray Consulting
Technical Editor

NEW YORK — I made a Facebook posting last week regarding a radio program I am involved with – Ron Ananian, The Car Doctor.  A friend who has a voice over business posted that he’s heard the show through one of his clients and thought it was a good show and sounded really good.  I posted back that I bet he never would have guessed we deliver the audio to the satellite uplink via an IP codec.  Another voice over friend chimed in wanting to know what codec we were using.  My first friend then said, “what’s an IP codec?”  Uh, oh.

Back in the “good old days”, if you wanted to get audio from point A to point B you had basically two choices: a dedicated land line from good old Ma Bell (aka, the phone company) or you sent a tape.

Then, Ma Bell decided to get rid of dedicated equalized services – at least interstate.  These days, it’s very difficult if not impossible to get a dedicated broadcast service even in the same city.

This prompted devices like the Comrex two line and three line frequency extender systems.  These allowed someone to utilize two or three dial up lines to get audio from one place to another with reasonable audio quality.

The next step was ISDN – a digital dial up service.  With the development of devices such as the Telos Zephyr, FM quality audio was easily passed, with very little audio delay, between two locations.  This has been the norm now for close to 20 years.

Enter the IP codec – essentially ISDN on steroids.  IP codecs utilize the Internet as the transport medium.  Now, for just the cost of the Internet service you already have installed, you can literally transport audio all around the world – in many instances with slightly more round trip delay than with ISDN, but that is easy to work around using mix minus.

The nice thing about most of the IP codecs available is that you can choose from numerous algorithms – these define the type of digital coding used in the digital to analog and analog to digital transition and how the transport over the Internet works.

Depending on many circumstances, you can get CD quality audio, as a rule, over an IP codec connection.  The data rate is the rate at which the resulting audio stream is reduced in size – it also determines how much degradation from the original audio will occur.  A faster data rate will result in better sounding audio.  But a faster stream may also be prone to glitching if there is congestion on the Internet.  It becomes a balancing act – though all the IP codecs available have some type of error correction to try to prevent this.  Of course, this is real time audio we are talking about, not computer streaming which is similar but a very different animal, so there is only so much error correction that can be done before the round trip delay becomes ridiculous and difficult to work with on a live program.

In many parts of the US, it is becoming more difficult to have ISDN installed, and where you can get it installed, it is becoming expensive.  The reason is that the phone companies are converting to IP connections in their central offices.  If they extend this IP connectivity beyond the central office, they can cut their costs dramatically.  In most cases, if a local phone company updates the equipment in a central office, ISDN is no longer being offered.

ISDN was the answer to high speed Internet in the “stone age” of the 1990’s.  The maximum guaranteed speed of 128 kilobits was lightning fast back then – compare that to the 5 megabits you get today on your DSL or cable modem Internet connection.  Broadcasters picked up on ISDN as a transport mechanism for digitized audio.  Banks picked up on ISDN for ATM connections.  Today, most ATM’s are connected via the Internet, either hard wired or through a cellular connection – next time you hit the ATM at the mall or at a movie theater, look carefully at the top of the unit.  You will probably see an antenna.  With banks getting away from ISDN, that pretty much leaves broadcasters using the service.  In many areas, building ISDN connectivity into a central office becomes a revenue loser for phone companies.  So, they’re doing away with it.

IP codecs are definitely the way to go.  It’s flexible.  It’s inexpensive to transport the audio.  It sounds better in the majority of cases than ISDN.  And there are several different manufacturers that are interoperable, ie, their IP codec boxes will play nicely with each other.  With a device such as the Comrex Access portable unit, you can even do an entire remote on a 4G cellular connection.  I know.  We did several on WOR – we’re talking the New York market here – over the past few years when we could not get ISDN and did not even have reliable dial up available.

IP codecs are here, are viable, and work very well.  If you’ve had butterflies about relying on the Internet to get your audio from point A to point B, it’s time to put those fears aside.  And if you are working with numerous clients, like voice over people do, it is a very cost effective and high quality way to work in real time with your client to get the job done.

Editor’s Note:  Read Tom’s follow-up piece on this subject here.


Thomas R. Ray, III CPBE, AMD, DRB is president of Tom Ray Consulting and Technical Editor of TALKERS. He can be phoned at 845-418-5065 or emailed at  His website is  Meet Tom Ray at TALKERS New York 2013 on Thursday June 6. 

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Category: Technical