Technology: Matsushita gets rough on Mini Disc

By BARRY FOX Japan’s giant of consumer electronics, Matsushita, has set the stage for a repeat of its ‘video war’ with Sony – this time over audio digital recording. At a private technical seminar last week engineers from Matsushita’s headquarters in Osaka staged experiments designed to expose technical defects in Mini Disc (MD), Sony’s digital audio system. They also played up the benefits of the Digital Compact Cassette system, developed by Philips of the Netherlands. Matsushita sells DCC systems through its Technics and Panasonic subsidiaries, and has been closely involved with DCC’s development since 1989. Although Matsushita has long been a rival of Sony, it usually avoids public wrangles. Almost two decades ago its technically inferior but more popular VHS video system defeated Sony’s Betamax. However, the issues involved in the ‘audio war’ are less clear. Sony has emphasised that MD is more portable, resilient and easy to use than CD players and especially DCC players. But now Matsushita is trying to force the battle into one of sound quality. Although DCC uses magnetic tape, and MD uses discs coated with a magnetooptical medium that makes them erasable, both systems rely on data compression to reduce the number of bits per second that they record. Philips’s system reduces the number of bits by 75 per cent, while Sony’s reduces it by 80 per cent. Matsushita’s first tests analysed MD and DCC recordings of test tones and of square wave pulses, which are theoretically the sum of every frequency. These showed that DCC was faithful up to the extreme limit of human hearing, around 20 kilohertz, while MD reproduced little sound over 15 kilohertz – though this is the limit of most people’s hearing. Tadashi Abe, general manager in charge of Matsushita’s DCC development, says ‘The sound disappears, making it more like FM radio than digital audio.’ Abe believes that DCC copes better with high frequencies, and sounds ‘brighter’, because its encoding splits the sound into more frequency bands before analysing them, thereby making better use of the available bits. Abe also recorded music from a CD onto both DCC and MD, and then copied the copies. (Domestic users could not do this because of anti-piracy circuits built into their systems.) Abe showed that in MD the process exaggerates any distortion introduced by the recording circuitry. Even after one extra copy, MD added a rough edge to the sound of a solo trumpet. After 10 copies, a harpsichord sounded like an old bar-room piano. In each case DCC did comparatively little damage to the sound. Abe’s most telling test subtracts a recording made using data compression from the original music. This leaves a difference signal which represents the musical content omitted by the compression circuit. When DCC was used to record castanets, which produce percussive high frequency sounds, the difference signal was a light rhythmic tizz. With MD the difference signal was louder and stronger, showing that the compression circuit had omitted more musical content. A spokesman for Sony, which had no advance warning of the tests, says:
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