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High-pass "hum" filter
This filter removes hum and other unwanted low frequency noise from the caller audio. This
filter has a crossover frequency of 250 Hz.
Receive Automatic Gain Control
This AGC serves to improve consistency of caller audio levels. This function is very
important to effective hybrid performance as caller levels can vary by as much as 30 dB. This
AGC is an advanced dB linear feed forward topology providing a consistent sound
independent of drive level. Its "smart" response normalizes levels while retaining the natural
dynamics of the caller's voice.
An important additional feature of this AGC is that it is cross-coupled to other sections of the
Studio Interface and can therefore reliably distinguish between caller audio and hybrid
leakage. This allows a more aggressive gain control for bringing up low-level callers while
still preserving excellent hybrid performance.
Noise Gate
Turning on the noise gate enables the built-in downward expander. The downward expander
reduces low level line noise when no caller audio is present. And reduces low level leakage
thereby improving hybrid performance. This function is cross-coupled with the AGCs and the
duplex system.
Digital Dynamic Equalizer
Telephone audio frequency response varies widely as many different factors can affect it
(we've measured the response on a number of calls and the results were revealing).
Consequently, some form of receive equalization is desirable. See section 3.3.1 for details on
how to adjust the DDEQ system.
The Digital Dynamic EQ process used on the Telos is the most sophisticated equalizer
available in a telephone hybrid. The purpose is to allow you to customize the sound of callers
on your station. All processing is performed in the digital domain. The Receive EQ selection
controls the type of equalization applied to the receive telephone audio as follows:
Off
The caller audio is passed without modification. The Rcv EQ values (see below) are ignored
in this mode.
Fixed
This is a simple manual equalizer mode where EQ values selected for LF and HF are applied
constantly.
Adaptive (Digital Dynamic)
This is a three band dynamic equalizer. The proper values of high and low frequency boost or
cut is automatically determined and set. We've chosen frequency breakpoints, time constants,
and other characteristics to optimize the tonal quality of varied telephone callers. The Rcv EQ
values (see below) are ignored in this mode.
Fix + Adap:
THE STUDIO INTERFACE & ADDITIONAL HYBRIDS
SECTION 3 – STUDIO INTERFACE: DETAILED CONFIGURATION & REFERENCE
TELOS 2101 USER'S MANUAL
PART IV
IV-85
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