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Hybrids, Codecs, and Encoders - What's the Difference?

By Matt Rockwell on Dec 31, 2012 11:51:00 AM

We sometimes get asked: what's the difference between hybrids, codecs and stream encoders? Let's take a moment and talk about how these different technologies.


In the broadcast world, a Telephone Hybrid is needed in place of a telephone handset to connect a caller to air. The phone mixes (or duplexes) both incoming and outgoing audio together so that the phone company only needs to transport a single audio channel.

As broadcasters, we would like to have two audio channels on the hybrid: in and out, just like a phone has a mic and an earpiece. Discrete audio is preferred so that the audio is mixed in the console instead of the phone line. Mr. Steve Church, founder of Telos Systems, was the first person to figure out how do do this with digital signal processing instead of analog circuitry. Cool!

The phone companies caught onto the idea of using digital transmission instead of analog and (mostly) standardized digital signals over the same copper telephone wires using ISDN technology back in the '80s. Since there are a gazillion phones in the world, and ISDN phone circuits can be connected to regular telephone lines, the phone company handles the switching. A caller can call from their telephone to a radio station's hybrid and be heard "on the air" cleanly and without echo using the same copper phone lines.

Here is a comparison of the various Telos-brand hybrids used for communicating with callers via POTS, ISDN, and even SIP circuits as well as the features of each.


An audio codec in broadcast is a device or used to connect remote audio to the broadcast when a device can be specific at each end of the connection. Since both ends of the connection are on common devices, it it's possible to specify the audio codec used. The Zephyr, Telos' first codec, was the first device to use .MP3 audio encoding to deliver superior sounding audio over the same ISDN lines. Codecs sounded much superior to what could be achieved with a hybrid.

The voice tracking community uses codecs frequently and extensively to be able to transmit high quality audio real-time over great distances. In the broadcast world, a connection of this type is often referred to "zephyring" in honor of Mr. Church's first codec, the Zephyr.

Now, Telos offers codecs for both ISDN and Internet-IP connections. The Zephyr Xstream is the current incarnation of the classic Zephyr, AND still compatible all around.  The classy Z/IP One is a modern 19" 1U Internet codec which is even capable of making high quality connections over 3g wireless connections.

Stream Encoders

An audio encoder, in the broadcast realm, typically refers to a stream encoder. Quite simply, the stream encoder makes a digital "stream" source which can be relayed to end listeners via the Internet as an alternative to traditional terrestrial radio signals. When one clicks on a "listen" link at a station's website or listens to Pandora, the data flows continuously from the stream encoder to the listening device, and there are all manners of ways of doing this.

The Telos Alliance has streaming audio hardware and software called "Z/IPStream." The approach of these tools is:

  • Receive stereo input audio as analog or Livewire
  • Process the audio both for best listening and for proper encoding
  • Encode with authentic Franhaufer codecs
  • Embed the station and current play metadata
  • Deliver the audio to a public streaming server for replication and delivery

 Live audio is alive and well in the Internet age, thank you very much!

Topics: Telephone Hybrids


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