Technology: And now, over to my front room

 作者:盛赴     |      日期:2019-02-28 04:19:01
By BARRY FOX If you were thinking up a list of occupations that could be done by telecommuting, would it include radio broadcasting? Probably not – but a growing number of radio personalities are exploiting the potential of new digital compression techniques. These have improved sound quality so much that they can broadcast from their living room, an interview room at a sports stadium, or (given enough warning) the back room of a restaurant. After tests last year (Technology, 4 September 1993), Quentin Howard, a presenter on Classic FM, now routinely broadcasts live from his home in Wiltshire, and even plays his own CDs down the line to the studio in Camden Town, London. When Jonathan Dimbleby hosts Any Answers? on BBC Radio 4, he is usually broadcasting from home. When Gary Glitter and Samantha Fox broadcast live last year to listeners in New York, they were talking by phone from the Criterion Theatre and Bill Wyman’s Sticky Fingers restaurant in London. Similarly, Bob Dylan, the rock group Bon Jovi and guitarist Ry Cooder performed in concert with Buddhist monks at the end of May. The sound heard by radio listeners round Europe had first travelled by telephone line from a temple in Nara, Japan, to BBC Broadcasting House in London. The BBC also now uses telephone lines to relay the Proms from the Albert Hall. The shift has been made possible by two parallel developments. First, to encourage businesses to use the ISDN (Integrated Digital Services Network) system to carry digital signals between computers, video conference cameras and high-speed fax machines, British Telecom now charges the same rate for a digital call as for an analogue one of the same distance. And the electronics industry has built coders which convert studio quality analogue sound into digital code and compress it into a data stream which can flow down ISDN lines with no discernible loss of quality. Conventional twisted pair telephone lines carry an analogue audio signal with a bandwidth of less than 4 kilohertz, giving a ‘boxy’ sound when replayed on the radio. An ISDN line (which can be twisted pair over a short distance) carries two separate digital data streams, each running at 64 kilobits per second. Two rival compression techniques to fit the audio signal into an ISDN stream are fighting it out for adoption as a standard by the broadcast industry. One, called Musicam, was developed for digital audio broadcasting under the pan-European research and development programme, Eureka. The coder splits the analogue sound signal into 32 narrow frequency bands, and converts each separately into digital code. The other, APT-X, comes from Audio Processing Technology, a Belfast company. It splits the sound into four frequency bands, chops each into short time samples and encodes only the difference between successive samples. Both systems can compress data by a factor of four without loss of quality. Voice requires 64 kilobits per second; CD quality stereo requires a bandwidth of 256 kilobits per second, which can be obtained by using two ISDN lines together. Engineers cannot yet decide which system is best because the audible differences are subtle and vary with the data rates chosen. Musicam has more powerful compression, and can get better sound quality from very low data rates,