Digital Audio Broadcasting (DAB) refers to a radio broadcasting technology wherein radio programs are transmitted and received in digital form. Thousands of radio stations around the world are already broadcasting radio content in DAB format, but it is currently most widely accepted in Europe.

DAB systems apply multiplexing and data compression techniques to squeeze many audio streams into a single broadcasting frequency called the 'DAB ensemble'.  The transmitted DAB ensemble thus contains all the DAB radio channels or stations. 

Each DAB station in the ensemble is assigned its own bit rate, which depends on the type of content it is broadcasting.  A higher bit rate means better audio quality, so a DAB station that broadcasts CD-quality music must be given a higher bit rate than one that just broadcasts news reports in voice.  The assignment of bit rates must be planned well so as maximize the use of bandwidth, i.e., the ensemble must contain as many channels as possible without any channel giving up the audio quality that it deserves.

DAB technology has been around for decades, with the DAB standard being designed in the 1980's. The original DAB standard did offer some benefits in comparison with analog FM, such as increased immunity to noise and interference and a higher number of stations within an equivalent broadcast spectrum.  However, this original DAB standard failed to impress many radio listeners. In fact, tests conducted showed DAB radio at that time to be lower in audio quality versus FM radio.  This is because DAB is using an inefficient audio codec, the MPEG Layer 2, which could not provide CD-quality audio using the DAB bit rates.

To correct this situation, a new DAB standard, the DAB+, was released in 2007.  Now using the more efficient AAC+ audio codec, DAB+ technology has naturally proven to be more efficient in transmitting audio streams than the original DAB, allowing it to broadcast high-quality audio at a lower bit rate (as low as 64 kbits per second). It also incorporated a stronger error correcting code that makes the reception more stable.  Unfortunately, DAB+ is not compatible with DAB, which means that receivers designed for the original DAB standard only can not be used to receive DAB+ broadcasts. Still, more and more countries are now switching from DAB to DAB+.

    

Figure 1.  DAB music can be heard on a wide variety of radio receivers like this one.

   

Although DAB+ now offers better audio quality than DAB, it still can not be categorically said that they offer better audio quality than terrestrial AM and FM stations.  Sound quality is determined by the bandwidth available to a station, so some FM and AM stations are still better in audio quality than some DAB stations.

  

Nonetheless, the digital nature of DAB and DAB+ allows them to offer the following benefits over analog broadcasting:

1) improved user interface/experience - DAB can carry other types of data, allowing it to supply information like song titles, artist names, traffic updates, etc.;

2) lower cost of operation - the multiplexing and information processing techniques possible with digital broadcasting allow it to transmit many channels over a single transmitter efficiently;

3)  more radio stations for the same bandwidth - again, this is due to the fact that DAB allows many channels to be multiplexed efficiently into a single data stream;

4) better reception quality -  digital audio can be transmitted cleanly while error-correcting techniques can compensate for transmission problems;

5) immunity to interferences.

See Also:   More Industry Articles