AEV ITB 302 Evolution Руководство по эксплуатации - Страница 7

Просмотреть онлайн или скачать pdf Руководство по эксплуатации для Телефонная система AEV ITB 302 Evolution. AEV ITB 302 Evolution 17 страниц. Digital telephone hybrid

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Electronic Equipment

A telephone hybrid is a system that is able to make an audio connection between a telephone

line and low frequency equipment. In practice this connection is by no means simple since

the characteristics of the telephone line require the equipment to employ a series of

techniques to ensure good audio quality and immunity to interference.

The bandwidth of a normal telephone line is compressed from about 100 Hz to 3-4 KHz in

order to guarantee a good reproduction of the human voice. A telephone hybrid must have a

wide frequency response in order to adapt to the quality of any line and to avoid adding

further limitations to the system. Unfortunately telephone lines are often sources of intense

disturbances, noise, crackling, fading etc. Furthermore they are often sources or conductors

of static charge and overvoltage, able to destroy circuits which have been imprudently

connected to them. Add the fact that the resistive and capacitative behaviours of line are

not uniform, and thus barely repeatable, and clearly the transmitted audio quality will vary

with time.

It is therefore necessary to take particular care in the design of line-audio interfaces in order to

avoid significant degradation of the bandwidth or re-injection of induced interference. The

interface must also ensure complete electrical isolation between the line section and that

connecting to the audio equipment.

Another problem arises during a telephone connection between a remote correspondent

and an interviewer or DJ; the DJ's voice will be transmitted down the telephone line and,

since the same line is used for transmission and reception, received again with a delay

with respect to the original. It will be re-amplified and looped back resulting in whistles

and Larsen effects. Usually, antilocal circuits are designed to solve this matter by

identifying those audio components which tend to enter into the loop and eliminating

only the part which re-enters. This is indispensable for Audioconferences.

The new Digital Hybrid features with an electronic echo canceller, that allows to reduce

drastically or even eliminate the feedback. In this way the diaphony is improved thanks

to the use of a DSP.

Audioconferencing allows simultaneous communication between remote correspondents that are

interconnected through telephone lines and the hybrid, which interconnects them without

introducing distortions or noise. It allows also to the DJ to participate in the conference. The

DJ, as "manager" of the conference, is able to include or exclude each correspondent from the

conference and can also speak privately to each of them for instance to prepare the interview.

AEV ITB-302 is a telephone hybrid that satisfies all today's demands for studio and broadcast

telephony allowing total management of telephone lines. It is designed in a 19", 1 unit, rack-

mounting container, housing 1 or 2 telephone hybrids. Units may be interconnected to allow

expansion to "n" lines whilst maintaining simplicity of use and the possibility of remote control.

The telephone lines, appropriately filtered and isolated, allow Audioconferencing between them

and the DJ. An internal microprocessor provides a range of functions that, until now, have been

difficult to provide in the same unit. All potentiometers were eliminated in order to solve wear

problems. It is also available a socket on the rear panel to connect a headset.

ITB 302

Telephone hybrids

Features of AEV ITB-302

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