|DAB Explanation (Digital Audio Broadcasting)|
DAB/DAB+ can use VHF frequencies in VHF band around 50Mhz and 200Mhz. There is also some frequencies available around 1450Mhz.
As DVBT multiplex, each frequency can support many Radios at the same time.
It uses synchronous technology, which allows to use same frequency for transmitter sending same multiplex in the same area.
These frequencies are named "Blocks" and are named like "2A". Here is the list of blocks:
|2A||47.936 MHz||2B||49.648 MHz||2C||51.360 MHz||2D||53.072 MHz|
|3A||54.928 MHz||3B||56.640 MHz||3C||58.352 MHz||3D||60.064 MHz|
|4A||61.936 MHz||4B||63.648 MHz||4C||65.360 MHz||4D||67.072 MHz|
|5A||174.928 MHz||5B||176.640 MHz||5C||178.352 MHz||5D||180.064 MHz|
|6A||181.936 MHz||6B||183.648 MHz||6C||185.360 MHz||6D||187.072 MHz|
|7A||188.928 MHz||7B||190.640 MHz||7C||192.352 MHz||7D||194.064 MHz|
|8A||195.936 MHz||8B||197.648 MHz||8C||199.360 MHz||8D||201.072 MHz|
|9A||202.928 MHz||9B||204.640 MHz||9C||206.352 MHz||9D||208.064 MHz|
|10A||209.936 MHz||10B||211.648 MHz||10C||213.360 MHz||10D||215.072 MHz|
|11A||216.928 MHz||11B||218.640 MHz||11C||220.352 MHz||11D||222.064 MHz|
|12A||223.936 MHz||12B||225.648 MHz||12C||227.360 MHz||12D||229.072 MHz|
|13A||230.784 MHz||13B||232.496 MHz||13C||234.208 MHz||13D||235.776 MHz|
|13E||237.488 MHz||13F||239.200 MHz|
One DAB block can handle many Radios, each radio is independent. The total capacity of a DAB block is 864 "capacity units".
The provider of the block need to ensure that the summ of each radio capacity is not higher than 864 CU.
Each Radio choose its audio bitrate. The radio can add some datas (for ex traffic datas) on a new PID channel.
The DAB can also add datas on special reserved and normalized part, as for ex "radiotext (DLS)" with the current title and the "slideshow" who can transmit pictures.
The radio need also to choose it's transmit level protection. This protection is adding some datas on transmit part, to allow reception error cancelation in receiver.
The more highest is the protection, better will be the reception. Each radio in a DAB block can have different protection level.
The number of "Capacity units" of one radio is related to the audio bitrate, data bitrate, datas radiotext and slideshow and also by the protection level.
The DAB tables of Digitalbitrate have all these informations, and a multiplex graph is displaying the room used by each radio in term of capacity units.
The DAB is using MPEG1 layer 2 for audio encoding.
The DAB+ is using AAC to decrease bitrate needed and to increase sound quality.
The AAC has some audio encoding optimization features:
SBR: spectral band replication
PS: Parametric stereo
The Digitalbirate table is showing id SBR and/or PS are enabled.