A qualidade do som digital é má?

«Music lovers are calling on broadcasters to improve sound quality on digital radio after complaints that it is worse than traditional FM. Critics say the BBC and commercial broadcasters have crammed so many new stations into their digital transmissions that sound quality has been badly compromised. While the difference is barely noticeable on kitchen radios, owners of expensive hi-fi systems say digital sounds tinny and muffled.

About five million people listen to digital radio. The sets, usually costing between £70 and £130, are easier to tune, give access to dozens more stations and display channel and programme information. Many people also believe sound quality is better. But while digital transmissions have none of the hiss or crackle found on traditional radio, a vocal minority of hi-fi buffs argue that the sound quality is much worse than FM.»

MAIS: «The quality of a signal is measured by its "bit rate" - the number of pieces of information transmitted each second. A typical CD, for instance, has a rate of 256,000 bits per second (kbps). The best quality digital radio station is Radio 3 which usually transmits at 192 kbps. But Radio 1, 2, 4 and 6 are broadcast at 128kbps, while Radio Five Live is broadcast at 80kbps. To accommodate the part-time station BBC Five Live Sports Extra during sports events, Radio 4 drops to 80kbps and becomes mono, while Radio 3 reduces to 160kbps. Steven Green, a music journalist who campaigns about digital radio quality says such rates are "noticeably" worse than FM. "On a small portable, it is not an issue," he said. "But if you have very good FM reception on a hi-fi system, digital radio is worse." Radio 1 and 2 listeners suffered most. Music lacked definition and had a compressed dynamic range. "It's pretty nasty. I don't listen to digital radio."In analogue radio each station has a dedicated frequency. But with digital, several stations are transmitted together on one frequency in a package called a multiplex. There is a trade-off between the number of stations that can be broadcast on each multiplex, and the bit rate. When the BBC began its tests of digital radio in the 1990s, it broadcast all its major stations at 192kbps. But in order to introduce new channels - such as 1Xtra, Radio 6, Radio 7 and BBC Asian Network - it reduced the sound quality across the board.»

Mr Green says the BBC gains quantity at the expense of quality and is petitioning the corporation to raise bit rates through his website www.digitalradiotech.co.uk.

A BBC spokesman said: "The BBC has a responsibility to serve all its diverse audiences and we believe we have found a balance between launching new services and broadcasting in good sound quality.

"We believe we are providing good sound quality on all our digital radio networks and recent research bears this out. The majority of people are very satisfied with the sound quality with around 95 per cent of digital radio listeners rating it 'excellent', 'good' or 'satisfied'."

Mandy Green, of the Digital Radio Development Bureau, said the industry no longer promoted digital on sound quality. Only a small fraction of listeners were unhappy. Clare Newsome, the editor of What Hi-Fi? Sound and Vision, said: "If you are replacing a 20-year-old kitchen radio with digital, the bit rate is irrelevant."

Telegraph, "Digital radio sound 'is worse than old FM', By David Derbyshire Consumer Affairs Editor, (Filed: 16/01/2006)