Telephone Balance Unit

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A Telephone Balance Unit is a device to convert the unbalanced audio carried on a copper phone line to balanced audio signals. It will also strip out any DC components (eg. ringing signals / line power.)

They are most commonly encountered in radio stations, where 'phone-ins' from members of the public need to be inserted into the broadcast chain and in news environments, where reporters 'phone in' a report.

The abbreviation 'TBU' is commonly used in the UK. In the USA however, the term 'Telephone Hybrid' is more commonly used.