DAB vs DAB+
DAB stands for Digital Audio Broadcast, a technology developed in 1980’s as a solution for the exhausted bandwidth in FM and AM frequency ranges. AM and FM, which are analog methods of broadcasting, is replaced by digital broadcasting method DAB and its newer standard released in 2006. Countries all over the world use DAB broadcasting systems; more prominently, in Europe.
More about DAB
DAB works on combining two digital technologies. MUSICAM, which is a compression system, reduces the vast amount of digital information to be transmitted, and COFDM (Coded Orthogonal Frequency Division Multiplex) enables the transmission to be robust and receive signals reliably.
The compression method relies on removing inaudible sounds and frequencies to the human ear. For example, background sounds that are overpowered by primary sounds are disregarded in the compression process, making the effective transmission data amount much lower. In the COFDM method, the signal is split across 1,536 different carrier frequencies, and also across time. This process allows the receiver to reconstruct the original signal, even though some of the frequencies are interfered. Therefore, theoretically DAB can be used in environments prone to interferences resulting in bad reception conditions.
The interference effects observed in the FM technology, due to multiple paths taken by the signals, are avoided by the DAB. As a result, a much larger area can be covered with a single frequency, rather than covering geographical areas with different frequencies to prevent disruptions.
A DAB multiplex uses 2,300,000 ‘bits’ for transmission. About half of the volume is used for audio and data services, while there is a volume for the protection system for transmission errors. Each multiplex can carry a mixture of mono and stereo broadcasts, and data services, and the number of each depends on the quality required. Services can be varied throughout the day according to program schedules.
Advantages of DAB over other transmission methods are the improvement in the reception quality and the sound quality, variable bandwidths, and low costs of transmission. For users, additional features like Dynamic Label Segment (radio text) can be provided. With DAB, more channels can be transmitted because of the reduced crosstalk and interferences resulting in less reuse bandwidth and allocate frequencies more closely. Some DAB devices also support internet radio services.
Despite the advantages DAB poses some difficulties to the receivers, due to low quality error correction used in the transmission. Broadcasters minimize the bandwidth of a channel to increase the number of channels in the frequency ensemble, causing significant loss in quality.
More about DAB+
In 2006, DBM the authority regulating the DAB standards introduced new standards for the DAB transmissions. Newer audio CODEC and stronger error correction coding were adopted.
DAB devices are not forward compatible; that is, a DAB device cannot receive DAB+ signals. A firmware upgrade has to be added to enable the device to receive DAB+ signals.
DAB vs DAB+
• DAB+ is the upgraded standard of the DAB.
• DAB uses MPEG-1 Audio Layer 2 audio CODEC, while DAB+ uses the HE-AAC v2 audio CODEC (also known as eAAC+) and MPEG Surround audio format.
• DAB uses punctured convolutional coding for its ECC, while DAB+ uses Reed-Solomon coding, which is a stronger error correction coding.
• As a result, DAB+ has
– Better sound quality
– Better reception
• DAB transmissions are not compatible with new DAB+ devices.
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