Telos NX12 - Manual (Page 82)

72 | section 5
Automatic Gain Control/Platform leveler
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Noise gate
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Dynamic equalization
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Sample rate conversion
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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 break frequency of 100 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. The Nx12 offer a new
approach to AGC to accommodate the fact that loud callers have become just as great a prob-
lem as low-level callers. The AGC is reset for each caller to a neutral position. to most-rapidly
accommodate both low and high-level callers. The AGC has a range of up to +/- 12 dB. The
AGC is an advanced dB- linear feed-forward topology providing a consistent sound indepen-
dent of drive level. Its ‘smart’ operation normalizes levels while retaining the natural dynamics of
the caller’s voice. The default setting is FULL.
An important additional feature of this AGC is that it is cross-coupled to other sections of the
Nx12 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
ducking system.
Digital Dynamic Equalizer
Telephone audio frequency response varies widely as many different factors can effect it (we’ve
measured the response on a number of calls and the results were revealing). Consequently, some
form of receive equalization is desirable.
The Digital Dynamic EQ process used on the Telos is the most sophisticated equalizer avail-
able in a broadcast telephone interface. 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
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- The caller audio is passed without modification.
Fixed
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- This is a simple manual equalizer mode.
Adaptive
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(Digital Dynamic) - This is a three band dynamic equalizer. We’ve chosen
frequency breakpoints, time constants, and other characteristics to optimize the tonal
quality of varied telephone callers. The user-entered EQ values are used as ‘target levels’.
This allows you to customize the caller spectral characteristics, but still get a consistent
spectral characteristic from caller to caller.
Ducking System
The ducking function occurs primarily on the caller audio. This function is important for several
reasons:
Provides an “aesthetic” control over the caller that many programmers prefer. When the
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announcer speaks, the caller is ducked, or reduced in volume dynamically. This is particu-