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.