Telos TWOx12 - Why ISDN Makes Sense for Broadcast Talk Show Systems

TELOS TWOX12 USER’S MANUAL
INTRODUCTION
CHAPTER 1 2
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Automatic high-precision sample rate conversion for incoming ISDN circuits.
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Unmatched Send/Receive separation using Telos’ time-tested Adaptive
Cancellation technology. Each hybrid automatically & continuously adjusts to
phone line conditions, virtually eliminating the hollowness, feedback and
distortion that occurs when send audio “leaks” into the caller output signal.
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Sophisticated AGC/limiting functions and three-band Digital Dynamic
Equalization (DDEQ) ensure consistent caller audio levels and spectral
consistency.
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Easy to use menus. Full metering for proper setup and operation.
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Caller ID support and fully adjustable Caller Ducking (override) helps hosts stay
in control.
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Conference linking ability lets you set up high-quality conferencing between
callers with no external equipment needed. (Only a single mix-minus is
required.)
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Flexible system architecture allows you to buy an analog system now and
upgrade to ISDN in the future.
1.3 Why ISDN Makes Sense for Broadcast Talk Show Systems
ISDN is widely available, cost-effective, and offers many advantages for studio
systems. It is yet another example of digital technology enhancing broadcast
operations.
Integrated Services Digital Network (ISDN) is a set of international standards for
digital transmission over ordinary telephone copper wire (as well as over other
media). Presently, the dial-up telephone network is nearly entirely digital, except for
the “last mile” copper connections from the Central Office (Exchange) to the
customer’s site. Telos’ new ISDN hybrids take advantage of this technology to
deliver crystal clear caller audio to the radio studio.
Even though it takes two separate circuits — one send and one receive circuit — to
transmit telephone audio, traditional analog lines multiplex both circuits in order to
use a single pair of wires. This causes what’s referred to as “leakage” – when the
announcer’s audio is present on the hybrid output, creating an annoying “hollow” or
“tinny” sound. A “four-wire” circuit has two wire pairs, and therefore two
independent audio paths. Digital circuits are designed to always offer independent
and separated signal paths. (Though a digital circuit may today not use wires at all,
but rather fiber, or microwave radio, or satellite, telephone engineers, bowing to
tradition, continue to refer to all separated speech paths as being “four-wire.”)
The telephone network routes calls over 64 kbps channels. A sampling rate of 8 kHz
is used, with a word length of 8 bits. The 8 kHz sampling rate supports a Nyquist
(audio cut-off) frequency of 4 kHz. In practice, telephone systems are designed to
have audio frequency response extending to 3.4 kHz in order to allow relatively
simple roll-off filters to be used.