Astra Digital Radio (ADR) was a system used by SES for digital radio transmissions on the early Astra satellites, using the audio subcarrier frequencies of analogue television channels. It was introduced in 1995. As of February 2008, there were still 51 stations transmitting in this format.
Contents
Details
The format used one mono audio subcarrier, which was normally allocated to an additional audio track or radio station, or one channel of a stereo audio track/station. The carrier was digitally modulated and carried a 192 kbit/s, 48 kHz sampled MPEG-1 Layer II (MP2) encoded signal. 9.6 kbit/s was available for data.
Special receivers were required to listen to ADR stations, although some combined analogue/digital satellite boxes and later standard analogue boxes were equipped to decode it.
ADR was succeeded by DVB-S, with which it is incompatible, despite both being transmitted using MP2 and generally at the same bitrates. As a result, when the final analogue switch-off on the Astra 1 satellites occurred, ADR became obsolete.
The majority of the channels to have been broadcast using ADR were in the German language. In some ways, the system is seen to have replaced the Digitales Satellitenradio system, dating from the 1980s, which used an entire satellite transponder to carry 16 NICAM encoded radio stations, and which closed in 1999.