Digital Audio Broadcasting

Did You Know?

• Digital multimedia broadcasting (DMB) and DAB-IP are related standards developed for mobile radio and TV, supporting MPEG 4 AVC and WMV9 respectively as video codecs.
• DMB broadcasts in South Korea carry conventional MPEG 1 Layer II DAB audio services alongside their DMB video services.
• The BBC Research & Development department states that at least 192 kbit/s is necessary for a high fidelity stereo broadcast.

History and development

The DAB standard began as a European research effort in the 1980s, involving the West German Institut für Rundfunktechnik (IRT) and the French Centre commun d'études de télévision et télécommunications (CCETT). A consortium formed in 1986, with the BBC and other European broadcasters joining, and it became the Eureka-147 DAB Project in 1987. Its aims included better reception than FM, plus extra services like text, data, conditional access, traffic updates, and picture transmission. The first demonstrations were in 1988 at the WARC-88 conference in Geneva, followed by trials across Europe and a 1991 demo at the NAB Show in the US. The MPEG-1 Audio Layer II (MP2) codec was developed for this project. DAB was the first standard to use orthogonal frequency-division multiplexing (OFDM). In 1990, choices for audio codec, modulation, and error-correction were made, along with initial trial broadcasts. Frequencies were assigned to Band I, Band III, and L Band, separate from FM and AM bands. The protocol was finalized around 1992 or 1993, adopted by the ITU-R in 1994, the European community in 1995, and ETSI in 1997. The European DAB Forum (now WorldDAB) formed in 1995, and the Eureka-147 project ended, merging into WorldDAB in 1999. Pilot broadcasts began in 1995: Norway’s NRK launched the world’s first DAB channel on 1 June 1995, followed by the BBC and Swedish Radio in September, and a German pilot in Bavaria in October. Commercial UK stations started in November 1999 as Digital One.

Countries using DAB

Fifty-five countries provide regular or trial DAB(+) broadcasts. In the European Union, the European Electronic Communications Code (EECC) entered into force on 20 December 2018, requiring transposition into national legislation by 21 December 2020. Since the end of 2020, all new cars sold in the EU must have radios capable of receiving digital terrestrial radio. Belgium stopped sales of domestic analogue radio receivers from 1 January 2023 unless they also received DAB+. Norway was the first country to announce a complete switch-off of national FM radio stations, starting on 11 January 2017 and ending on 13 December 2017; local and community radio can continue on FM until at least 2031. In 2022, the Swiss government decided on a general FM switch-off by 31 December 2024, later extended to the end of 2026. SRG SSR, Switzerland's public-service broadcaster, shut down its FM transmission early on the original date, citing cost-effectiveness and widespread DAB+ adoption. After the switch-off, ratings researchers found SRG SSR stations lost between 20 and 30 per cent of their audiences. In December 2025, the Swiss parliament indefinitely postponed the full FM switch-off, and SRG SSR plans to restart FM broadcasts in fall 2026. Malta was the first European country to roll out a DAB+ network, covering 100% of the population since 2008. In Italy, Rai Radio proposes switching off FM transmitters starting in 2025 with a goal of all-digital by 2030; in South Tyrol – Alto Adige, broadcaster RAS has started switching FM services off.

Technology

DAB uses wide-bandwidth broadcast technology, typically allocated in Band III (174–240 MHz) and L band (1.452–1.492 GHz), though it allows operation between 30 and 300 MHz. The US military has reserved L-Band in the USA, blocking its use there, and the US has an agreement with Canada to restrict L-Band DAB to terrestrial broadcast. The current mode is Mode I for Band III, Earth; an updated specification in January 2017 removed Modes II, III, and IV. From an OSI model perspective, the audio codec inhabits the presentation layer, the data link layer handles statistical time-division multiplexing and frame synchronization, and the physical layer contains error-correction coding, OFDM modulation, and over-the-air transmission. DAB initially used the MPEG-1 Audio Layer II (MP2) codec. The newer DAB+ standard adopted LC-AAC and HE-AAC, including version 2 (AAC, AAC+, aacPlus), which uses a modified discrete cosine transform (MDCT) algorithm and is approximately three times more efficient than MP2. The choice of audio codec is critical because its efficiency determines how many radio stations can be carried on a fixed capacity multiplex at a given audio quality. Error-correction coding (ECC) determines how robust reception will be for a given signal strength.

Strengths and weaknesses

DAB devices perform band-scans over the entire frequency range, presenting all stations from a single list. DAB can provide metadata alongside the audio stream, including station name, logo, presenter, song title, and album artwork. It can carry radiotext (Dynamic Label Segment, or DLS) of up to 128 characters, similar to FM's RDS but with longer text. The transmission contains local time of day, allowing automatic clock correction when travelling between time zones or changing to/from Daylight Saving. DAB is not more bandwidth efficient than analogue in programmes per MHz of a specific transmitter (link spectral efficiency), but it is less susceptible to co-channel interference, allowing denser reuse of the same frequency. System spectral efficiency is about three times more efficient than analogue FM for local stations, and more than an order of magnitude better for national and regional networks using single-frequency networks (SFNs). In rural areas, DAB can increase listener choice; for example, in Southern Norway, available stations rose from 6 to 21 when DAB was introduced in November 2006. DAB integrates features to reduce multipath fading and signal noise. There is no hiss with a weak signal, but radios in fringe areas can experience a 'bubbling mud' sound or audio cut-out.