Digital Audio Broadcasting:-

Digital Audio Broadcasting (DAB), is a digital radio technology for broadcasting radio stations, used in several countries, particularly in Europe. As of 2006, approximately 1,000 stations worldwide broadcast in the DAB format.

The DAB standard was designed in the 1980s, and receivers have been available in many countries for several years. Proponents claim the standard offers several benefits over existing analogue FM radio, such as more stations in the same broadcast spectrum, and increased resistance to noise, multipath, fading, and co-channel interference. However, listening tests carried out by experts in the field of audio have shown that the audio quality on DAB is lower than on FM in the UK on stationary receivers, due to 98% of stereo stations using a bit rate of 128 Kbit/s with the MP2 audio codec, which requires double that amount to achieve perceived CD quality.

An upgraded version of the system was released in February 2007, which is called DAB+. This is not backward-compatible with DAB, which means that DAB-only receivers will not be able to receive DAB+ broadcasts. DAB+ is approximately twice as efficient as DAB due to the adoption of the AAC+ audio codec, and DAB+ can provide high quality audio with as low as 64kbit/s. Reception quality will also be more robust on DAB+ than on DAB due to the addition of Reed-Solomon error correction coding.
The reception quality on DAB can be poor even for people that live well within the coverage area. The reason for this is that the old version of DAB uses weak error correction coding so that when there are a lot of errors with the received data not enough of the errors can be corrected and a "bubbling mud" sound occurs. In some cases a complete loss of signal can happen. This situation will be improved upon in the new DAB standard (DAB+, discussed below) that uses stronger error correction coding and as additional transmitters are built.