RTS CS9500, User Manual

Page: 24 / 95

Smart
Digital
Automatic Gain control smooths input and output
levels. A expander is provided on the
receive path to reduce phone line noise during caller pauses.
A switchable function is provided to allow ducking of
the caller while the announcer is speaking. The function
includes an ducker which reduces send audio
when caller audio is present
in order to reduce feedback and aid
natural conversation.
Unique to the Telos One is a special feedback reduction function
using a pitch-shifting approach. The input (send) audio
is
downward in frequency by 4
Hz
to help prevent feedback build-up.
Front panel metering is provided for input level, output level,
and
gain
reduction.
Operation
When a call is initially established, a brief period
provides
an
opportunity for the system to set up to
the
line before
the call is passed to the output. The caller hears a "noisy tone,"
but none of this tone is heard at the output since the output is muted
during this time. This has the incidental benefit of removing the
line switching "clunk." to the telephone line
characteristic continues as the conversation proceeds using voice as
the driving signal.
The Hardware
The process of and digital-to-analog conversion
is
critical to audio quality and hybrid performance. In the Telos
One, IC converters
called
CODECS intended for telephone central
office application
are
employed. The ICs in the Telos One are
better than the usual telephone CODECS in that they use an
oversampling and digital filtering technique for the anti-aliasing
and reconstruction filters rather than the usual
filter approach.
Thus
noise and distortion are quite good.
Because the audio processing functions are performed in the digital
domain, the hardware design of the Telos One is quite simple.