Tech Notes
A Telecommuting Primer for Talk Hosts
With the introduction of new technologies, increasing numbers of radio talk hosts are getting out of the radio station studio and doing their shows from home or while travelling. ISDN and POTS codecs are the two products which have made this possible. With these codecs, talk hosts can sound like they are in the studio, interacting seamlessly with callers... and be almost anywhere in the world.
First, a little preliminary vocabulary lesson:
ISDN and POTS refers to the type of telephone service used. ISDN stands for Integrated Services Digital Network. ISDN is a digital dialup telephone service that is ordered from the phone company and is fairly widely available throughout the world. POTS stands for Plan Old Telephone Service. POTS is also sometimes referred to as PSTN or Public Switched Telephone Network. This is the normal business or residential dial telephone service. CODEC stands for COder/DECoder. This is the actual equipment that connects to either ISDN or POTS to send and receive studio quality audio.
ISDN and POTS codecs both have their advantages and disadvantages.
A short list is below:
- ISDN Advantages:
- Best quality audio
Consistent performance - ISDN Disadvantages:
- More complicated to setup
ISDN service may not be available / more $ - POTS Advantages:
- Flexible, Easy-to-use
Phone service costs less - POTS Disadvantage:
- Performance dependent on line quality
From a fixed location that is used often, such as a host’s home, ISDN is definitely the best choice because it will provide greater reliability. ISDN lines always carry a guaranteed data rate, unlike POTS lines which can vary significantly from call to call. Comrex makes two ISDN codecs which are widely used by talk hosts. Both deliver 15 KHz low-delay, two-way, mono audio on an ISDN line. The Nexus ISDN Codec is very compact and simple to use. There are connections for a microphone, headphone and an ISDN line. The Envoy adds a four channel mixer with three headphone feeds and an additional PA output to create a complete ISDN remote studio. The Matrix provides two inputs and outputs and, with the optional ISDN module, will work on either ISDN or POTS lines
POTS codecs can be great and usually their performance is comparable to ISDN. However there are some cautions to heed with this new technology. The performance of POTS codecs depends on the quality of the telephone line dialed.Outside influences on telephone lines (noise, crosstalk, etc.) can cause the modems in POTS codecs to fail during a broadcast, producing several seconds of muted audio while the modems reestablish the link. The Vector POTS Codec contains the same studio feature as the Envoy and delivers 15 KHz audio at 24 Kb/s or higher and drops to 5 KHz at 9600 baud. The BlueBox, Vector and Matrix deliver 15kHz audio at 24 kb/s.
Note: Some POTS and ISDN codecs have roundtrip coding delays of a second or more. These are not suitable for live interactive programs such as talk. The Comrex Envoy, Nexus, Vector, BlueBox and Matrix all have small coding delays and as long as a mix-minus feed is sent from the studio to the host’s site, there will be no noticeable delay in interacting with callers.
Suggested equipment list
(The microphone and headphone models are only offered as suggestions of commonly used broadcast items. For best quality, avoid consumer/pro-audio products.)
ISDN Setup
Host’s location:
Envoy or Nexus ISDN Codec (portable)
Microphone & Headphones
(see below)Studio:
Nexus ISDN Codec or Matrix with ISDN Module (rackmount)
(or any ISDN codec that works in G.722)
POTS Setup
Host’s location:
Matrix, Vector or BlueBox POTS Codec (portable)
Microphone & Headphones
(see below)Studio:
Matrix, Vector POTS Codec (rackmount)
Microphone
(e.g. EV 635A or EV RE20)
Headphones
(e.g. Sony 7504 or AKG K141or K240)
NOTE: For situations requiring the versatility of having both POTS and ISDN capability in one unit, the Matrix may be a good choice. The Matrix has two microphone inputs, one headphone output and a second auxiliary output. An optional slide-in module converts the Matrix into an ISDN codec.
The following documents provide further suggested reading and are available in the Tech Tips section of our web site: www.comrex.com.
Matrix POTS and ISDN Codec
Envoy ISDN Codec
Nexus ISDN Codec
Vector POTS Codec
BlueBox POTS Codec
POTS vs ISDN
Coding Delay
Mix-Minus
Home | Products | Support | Where to Buy | Press Room | Company | Contact