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<< The following questions have been culled from
those asked most often over the years. Most are from broadcasters, but
we feel that the answers are also relevant to similar problems encountered in
teleconferencing, distance learning, and other applications. If you have a
question you think should be on the list, please email support@telos-systems.com
.>>
The voices
of our announcers sound different when we have our older
telephone hybrid turned on. Is the hybrid to blame?
Good question. Many overlook this problem when evaluating their
telephone interface system. Indeed, the quality of the caller
audio and the ability of the hybrid to create full-duplex audio
are critical. But announcer voice distortion, caused by poor
trans-hybrid loss, is a key indicator of hybrid performance.
I've heard
the phrase "trans-hybrid" loss. Exactly what is it?
When the announcer speaks, his voice travels through the
hybrid's phone line output, to the caller, and back to the
studio into the hybrid's telephone line input. (You can hear
this "leakage" in the earpiece of your telephone
handset. Just listen to how much of your own voice comes back to
you!) Trans-hybrid loss is that portion of the announcer's voice
that leaks through the hybrid to its audio output. This leakage
is distorted and phase shifted after its long journey. Ideally,
the output of the hybrid should consist of the caller audio
only.
Just how
does trans-hybrid loss cause announcer distortion?
In a broadcast studio, the announcer audio is mixed at the
console with the hybrid (caller) output to create the
"on-air" mix. When you use a poor hybrid, its output
includes a distorted, phase shifted version of the announcer
signal. When this "leakage" is combined with the clean
announcer audio, a "hollow" or "tinny" sound
is produced as some frequencies are more affected by phase
cancellation than others.
The greater the trans-hybrid loss, the less announcer audio that
leaks into the hybrid output and the less the announcer voice
distortion.
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| The diagram on the right shows the
potential problems caused by poor hybrid performance. Telos' all
digital approach reduces announcer mic distortion and speaker
feedback while enabling natural sounding, two-way conversation
on-the-air. |
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Are there
any other problems caused by poor trans-hybrid loss?
Unfortunately, yes. In systems using multiple hybrids to
conference several callers, poor trans-hybrid loss will cause a
serious "singing" feedback, especially on low-level
callers. Poor trans-hybrid loss can also cause feedback when the caller
must be heard on an open speaker in the studio.
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