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Now you
really have my attention. We must listen to callers on open
speakers. Can we do that with Telos hybrids?
We pay very close attention to the problem of monitoring callers
through open speakers. In addition to excellent trans-hybrid
loss providing the first line of defense against feedback, our
DSP includes a two-stage, feedback reduction process we call
Digital Echo Elimination. The first stage is digital dynamics
processing that intelligently and instantaneously determines
appropriate gain values in the send and receive paths. The
second stage is a subtle, inaudible pitch shift to the input
audio before it is sent to the telephone line. The two elements
of Digital Echo Elimination significantly reduce the potential
buildup of feedback.
How does
Telos get results that are so much better than other hybrid
manufacturers?
Hybrids must deal with complex and erratic phone line impedance
characteristics across the phone line's frequency range.
Impedance variations are caused by nearly every piece of
equipment and run of cable between your studio and the caller's
telephone. To cancel the send audio, primitive analog hybrids
use simple resistor-capacitor "balancing networks" to
attempt to match the impedance of the phone line. It is a rare
phone line that has a smooth, unvarying characteristic, so
analog hybrids are often hopelessly ineffective.
How does
Telos' digital processing hybrid work?
Superior trans-hybrid loss is achieved using our advanced
digital signal processing (DSP) technologies. All functions are
totally in the digital domain. We have found ways to fine-tune
the adaptive process to achieve very fast nulling, stability of
adjustment, and, of course, maximum trans-hybrid loss. No other
analog- or digital-hybrid equipment comes close.
To offer a technical description: Telos digital hybrids use a
very advanced time-domain convolutional adaptive filter
algorithm to synthesize a transfer function for the balancing
network. A feedback loop continuously adjusts the filter to
conform to changing line impedances. In the Telos ONE, an error
signal is used to adjust the amplitude and phase cancellation
signal at a large number of frequency points. In the Telos 100
Delta, a gradient search technique is used to minimize the
discrepancies between the synthesized transfer function and the
telephone line's transfer function. The result is a very close
match to the phone line impedance curve for optimum rejection.
Must I
manually adjust the hybrid so that each call begins with optimum
trans-hybrid loss?
Telos hybrids perform all adjustment automatically and require
no "tweaking" once installed. When a call is initially
established, a brief mute/adapt period (between one-quarter and
one-half second) causes the system to adjust to the phone line
before that call goes on the air. The caller hears a "noisy
tone," but the tone is not heard on the air because the
hybrid output is muted during this time. This muting has the
incidental benefit of removing the line-switching
"clunk." As the conversation proceeds, adaptation continues, using the send audio as the driving signal.
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Why is
this dynamics control so critical?
Levels from caller to caller can vary as much as 30dB. The smart response of the gain control in our hybrid products uses the least amount of processing required so that the natural characteristics of the caller's voice are retained. To further achieve this end, the 100 Delta has a digital, logarithmic (dB linear) compressor that uses a feed-forward topology. This sophisticated compressor provides level-independent operation for outstanding performance regardless of caller level. |
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