Editing Digital Audio Broadcasting (section)

====Error-correction coding====
Error-correction coding (ECC) is an important technology for a digital communication system because it determines how robust the reception will be for a given signal strength – stronger ECC will provide a more robust reception than a weaker form.

The old version of DAB uses punctured [[convolutional coding]] for its ECC. The coding scheme uses unequal error protection (UEP), which means that parts of the audio bit-stream that are more susceptible to errors causing audible disturbances are provided with more protection (i.e. a lower [[code rate]]) and vice versa. However, the UEP scheme used on DAB results in a grey area in between the user experiencing good reception quality and no reception at all, as opposed to the situation with most other wireless digital communication systems that have a sharp "digital cliff", where the signal rapidly becomes unusable if the signal strength drops below a certain threshold. When DAB listeners receive a signal in this intermediate strength area they experience a "burbling" sound which interrupts the playback of the audio.

The DAB+ standard incorporates [[Reed–Solomon error correction|Reed–Solomon]] ECC as an "inner layer" of coding that is placed around the byte interleaved audio frame but inside the "outer layer" of convolutional coding used by the original DAB system, although on DAB+ the convolutional coding uses equal error protection (EEP) rather than UEP since each bit is equally important in DAB+. This combination of Reed–Solomon coding as the inner layer of coding, followed by an outer layer of convolutional coding – so-called [[concatenated error correction codes|"concatenated coding"]] – became a popular ECC scheme in the 1990s, and [[NASA]] adopted it for its deep-space missions. One slight difference between the concatenated coding used by the DAB+ system and that used on most other systems is that it uses a rectangular [[byte interleaver]] rather than [[Forney interleaving]] in order to provide a greater interleaver depth, which increases the distance over which error bursts will be spread out in the bit-stream, which in turn will allow the [[Reed–Solomon error correction|Reed–Solomon]] error decoder to correct a higher proportion of errors.

{| class="wikitable sortable"
|+ {{nowrap|Equal Error Protection}}<ref name="ETSI EN 300 401 V2.1.1" />{{rp|p=43}}<!-- notation e.g. 1-A used here, while in other similar standards e.g. EEP-1A seems to be more common -->
! class="unsortable" | Profile
! [[Code rate]]
|- <!-- data-sort-value max chosen 2520=2³·3²·5·7 for hypothetical 1/1 in order to get smallest integer exact values -->
| EEP-1A || data-sort-value=630  | 2/8 (1/4)
|-
| EEP-2A || data-sort-value=945  | 3/8
|-
| EEP-3A || data-sort-value=1260 | 4/8 (1/2)
|-
| EEP-4A || data-sort-value=1890 | 6/8 (3/4)
|-
| EEP-1B || data-sort-value=1120 | 4/9
|-
| EEP-2B || data-sort-value=1440 | 4/7
|-
| EEP-3B || data-sort-value=1680 | 4/6 (2/3)
|-
| EEP-4B || data-sort-value=2016 | 4/5
|}

The ECC used on DAB+ is far stronger than is used on DAB, which, with all else being equal (i.e., if the transmission powers remained the same), would translate into people who currently experience reception difficulties on DAB receiving a much more robust signal with DAB+ transmissions. It also has a far steeper "digital cliff", and listening tests have shown that people prefer this when the signal strength is low compared to the shallower digital cliff on DAB.<ref name="autogenerated1" />