TELOS TWOX12 USER’S MANUAL
INTRODUCTION
CHAPTER 1 4
Lower Noise
Because they are digital circuits, ISDN lines are not susceptible to induced noise.
Analog lines are exposed to a variety of noise and impulse trouble-causers as they
move across town on poles and through your building. Hum is the main one, given
most line’s proximity to pole transformers and power lines, but there are also sources
of impulse noise from motors, switches, and other sources. Digital lines convey the
bits precisely and accurately from the network to your studio equipment without any
perturbation–so the audio remains clean. Even when the caller is using an analog
phone line to call in, the noticeably quieter digital connection between the hybrid and
the telephone network helps the hybrid achieve better rejection of outgoing audio
leakage.
Call Setup and Supervision are Better
Analog lines use a strange mix of signaling to convey call status. Loop current drop
and returned dial-tone signal that a far-end caller has disconnected; blasts of 100
volts at 20 Hz mean someone wants you to answer. Why should we be using a
mechanism designed to bang a hammer against a metal bell to transmit network
status information into the 21
st
Century? ISDN uses a modern digital approach to
controlling calls and conveying status information about them. The sophisticated
transactions on the D channel are able to keep both ends of a call accurately informed
about what is happening.
For starters, ISDN call set-up times are often only a few 10’s of milli-seconds,
enhancing production of a fast-paced show. Perhaps more importantly, when a caller
disconnects while waiting on hold, the ISDN channel communicates this status
change instantly. This contrasts with the usual 11-second delay on most analog lines.
One of the most common complaints of talk hosts is that they go to a line where they
expect a caller to be waiting, only to be met with a blaring, annoying dial tone. The
chance of this happening with an ISDN line is nearly zero.
Another common error is the condition where a talent punches-up a line that looks
free, but which actually is just about to begin ringing and connects to a surprised
caller. This condition, called glare, results from the delay in the ring signaling, which
comes from the nature of the analog line’s ringing cadence. This is much less likely
with ISDN because it eliminates the ambiguous status period.
?
CURIOSITY NOTE!
We don’t know why the condition of picking up a line which was about to ring and
getting an incoming call instead of dial tone is called “Glare”. Perhaps its because the
looks air staff give engineers when this happens too often!
If you find out, be sure to let us know!
Higher Gain and Reduced Feedback During Multi-line Conferencing
Higher Gain and Reduced Feedback During Multi-line Conferencing. When
conferencing is required on 2-wire circuits, very good hybrids are needed to separate
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