programmes such as the Six O'Clock News and Midnight News, and news programmes such as Today, The World at One and PM, which by early 2013 had returned to Broadcasting House after 15 years at BBC Television Centre in White City. The news returning to Broadcasting House has also meant that newsreaders can provide cover for continuity, which regularly occurs at 23:00 each night and 16:00 on a Sunday. This has reduced the total number of continuity announcers required each day down from four to three. The Greenwich Time Signal, popularly known as "the pips", is broadcast every hour to herald the news bulletin, except at midnight and 18:00, and 22:00 on Sunday, when the chimes of Big Ben are played. There is no Greenwich Time Signal at 15:00 on Saturday or 10:00 and 11:00 on Sunday due to the Saturday Afternoon drama and the omnibus edition of The Archers respectively. Only pips broadcast on FM, MW and LW are accurate. On digital platforms there is a delay of between three and five seconds, and up to 23 seconds online. Programmes Radio 4 programmes cover a wide variety of genre including news and current affairs, history, culture, science, religion, arts, drama and light entertainment. A number of the programmes on Radio 4 take the form of a "magazine" show, featuring numerous small contributions over the course of the programme—Woman's Hour, From Our Own Correspondent, You and Yours. The rise of these magazine shows is primarily due to the work of Tony Whitby, controller of Radio 4 from 1970 to 1975. The station hosts a number of long-running programmes, many of which have been broadcast for over 40 years. Most programmes are available for four weeks after broadcast as streaming audio from Radio 4's listen again page and via BBC Sounds. A selection of programmes is also available as podcasts or downloadable audio files. Many comedy and drama programmes from the Radio 4 archives are broadcast on BBC Radio 4 Extra. Due to the capacity limitations of DAB and increasing sport broadcasts on BBC Radio 5 Live Sports Extra, BBC Radio 4 DAB has to reduce its bit rate most evenings, such that after 7 p.m. its DAB output is usually in mono, even though many of its programmes are made in stereo (including its flagship drama "The Archers"), these can be heard in stereo only on FM, Digital TV on