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STAC Product Manual
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Simply put, a hybrid is a device that separates send and receive audio on a
phone line. While the public switched telephone network utilizes separate
channels for audio in each direction of a phone call, these two signals are
mixed together before being sent to the end user. This way, only one pair
of wires is required from your telephone to the telco central office. To use
telephone company terms, the telephone network is a “four wire” system,
while the local loop is a “two wire” system.
When recording or airing telephone conversations in a studio environ-
ment, it’s important that telephone audio be “four wire”. This is because
the audio program usually already contains the audio of the studio host.
If the telephone audio also contains some of the studio audio, these two
signals will be added together by the mixing console. The effect will be
distortion in the voice of the studio host. In essence, a hybrid converts the
“two wire” telephone line back into a “four wire” audio path.
It seems counterintuitive, but the main goal of a studio hybrid is to im-
prove the sound of the people in the studio, not the callers. If the hybrid
isn’t working well, people speaking from the studio will sound “hollow”
or like they’re “talking into a barrel”. This is due to the strange effect of
mixing microphone audio with telephone “bleed-through”. Of course, our
hybrids also improve the audio of callers, filtering out hum and noise as
well as adjusting levels between loud and soft speakers.
It is our opinion that with the advent of cheap telephones, cordless
phones and cellphones, telephone audio has gotten decidedly worse in
recent years. While a hybrid can clean up noise to some extent, it cannot
remove distortion caused by the far end telephone. If you find some calls
sound good on the air and some don’t, it’s probably due to the large dis-
parity in audio quality of today’s telephone sets.
STAC uses digital signal processing (DSP) technology to continually adapt
to telephone-line conditions – providing consistent, high-quality sound
and send-to-caller separation. The hybrids help bring uniformity and high
quality sound to a broadcast talk show environment.
STAC contains two digital hybrids. Only one STAC hybrid is used in nor-
mal use (e.g. contests, requests, interviews). Both hybrids are utilized only
when more than one call is on the air at the same time. This is done by
Locking
one call on the control surface (or STAC IP) and putting another
call on the air.
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