Requirement of high data rate bad news for DAB proponents
The digital radio system DAB+ , needs to transmit high data rate, otherwise there is a risk of poor sound quality. It is one of the conclusions of a research project where Luleå University collaborated with the Swedish public service radio (SR). The results are published in the latest issue of the "Journal of the Audio Engineering Society" and has also been submitted to the British Departement of Culture and Media which is expected in mid-December to announce a switch-off year for FM for major broadcasters.
This is bad news for the DAB lobbyists because in order to get as many channels as possible into one multiplex bit rate is limited to 32-128 kB/s (more than 10 channels). From when the DAB system was invented 1985 until it was put into operation 1995 the most important argument for this investment was the possibility to broadcast music "with CD quality". 2002 BBC stated in a policy document that 192 kB/s was the lowest limit for quality.
- We have indications that one would need up to 300 kilobits per second for a transparent system where you can not perceive a loss in quality, says Jan Berg, assistant professor at the Northern Sweden Luleå University of Techonology (LTU) who has been responsible for the research project.
The digital solution, DAB +, is comparable to the existing FM system in the radio down to 160 kilobits / second. During the speed, the performance noticeably. The project that has been ongoing for two years, and in which five people worked, several tests have been done where experienced listeners participated. They have assessed the sound quality according to international recommendations. The tests show that one should select data rates close to the maximum that is possible to get out of DAB +.
- If you want to compete with a really good FM system should be run DAB + at maximum 192 kilobits / second in order to be able to maintain the quality of typical sounds that occur frequently in radio, says Jan Berg.
A conflict of objectives highlighted in the research is the need for high data rates for good sound in digital radio, while you want to have room for more stations within the same bandwidth. - Therefore, this study is important for those who will make decisions on how the data rate to be appropriated, says Lars Jonsson, technology strategist at SR.
In the published article also noted that there are several services that offer audio encoded with high data rate and it also puts pressure on the digital radio's sound quality will not be outdone.
These results with processed audio dispel the notion that the sound quality presently possible via digital radio is found inferior by only a tiny minority of audiophiles, says Trevor Brook at Surrey Electronics in the UK. This new evidence, specifically examining everyday radio audio, supports the view that DAB has a role as a supplementary platform but could never prove satisfactory as the sole outlet over the airwaves.
The five involved in the research project are Jan Berg LTU, Christofer Bustad SR, Lars Jonsson SR, Lars Mossberg SR och Dan Nyberg at the Swedish National Laboratory of Forensic Science.