BOXTEL MKII CONNECTION PROCEDURE
| BOXTEL MKII CONNECTION PROCEDURE
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BOXTEL MKII CONNECTION PROCEDURE
12.1 HYBRID TELEPHONE THEORY
The telephone hybrid is a device capable of interfacing a telephone line with audio lines.
In other words, the audio
signals sent to the hybrid are received by the phone and vice versa.
The telephone hybrid is widely used in radio and television broadcasting ad it makes it possible to make simple audio
connections with remote workstations at a very low cost. The signal coming from the hybrid is managed like a normal
audio source.
Telephone hybrids work on the basis of the principle of separation of impedance, also filtering the power supply at 60V
usually present on the telephone lines.
In the simplest form, the hybrid is conceptually an acoustic coupler, i.e. a device that acoustically takes the signals from
the microtelephone. A telephone hybrid is actually a more complex device that can interface directly with the telephone
line and make the necessary separation to avoid interference.
12.2 THE TELCO, MIX-MINUS AND N-1 CONCEPT
A fundamental part of the use of a telephone hybrid, is the knowledge and proper use of the TELCO system, also called
CF Clean Feed, or N-1 and / or Mix Minus. All these terms identify the following situations:
The expression n-1 indicates, in professional audio, the audio return signal that is sent from the studio to one or more
remote sources, such as a telephone hybrid. This signal is often called audio return, RX or also mix-minus in English.
The expression n-1 refers to the
Henri Poincaré
recurrence principle, n - 1, and indicates the complete mixing of the
audio signals in the studio except the one received from the remote unit.
In conceptual terms, therefore, the remote unit
receives in return an audio signal that includes the entire product of the studio except its own signal.
Departing a little from the theory, the n-1 is often a single signal for all the remote units of a single programme.
Common
usage foresees the generation of two or three returns, assigned on the basis of which remote units must interact with
each other:
with the n-1, in fact, two units cannot hear each other.
Sometimes, the audio return is simply an auxiliary of
the audio mixer to which the signals to be sent to the remote unit are assigned, resulting in a signal that is used as a
return but that is not technically a n-1 (see next chapter)