DAB and DAB+ services use up their data capacity for a variety of reasons.
Transport Layer
Firstly, a limited amount of data is required to provide a framework for the carriage of the various broadcast services transmitted on the multiplex.
Programme Layer
Secondly, a larger amount of data is used to deliver the various station’s programme audio content, which, together with programme related and non-programme related text (as well as still images where broadcast) is encoded for transmission within the DAB multiplex.
Error Protection Layer
Thirdly, each multiplex uses additional data to make the transmission of each broadcast service robust against interference, using what is known as “error protection”. In the UK, three levels of error protection are available for both DAB and DAB+ services. These error protection levels are known as UEP 3, UEP 2 & UEP 1 for DAB services and as EEP 3A, EEP 2A & EEP 1A for DAB+ services. The original international DAB and DAB+ standards also include further (weaker) levels of error protection (UEP 5 & UEP 4 / EEP 5A & EEP 4A respectively), but these are not permitted for use in the United Kingdom. Just as each individual programme service can operate at its own individual bit-rate, each programme service can also operate using its own individual level of error protection.
The trade-off is between programme data rates, error protection levels and the total number of services carried. Higher audio quality services and / or services with higher error protection levels each need a greater total amount of data when compared to lower audio quality services and / or services using a lower level of error protection.
The standard (lowest) level of error protection which must be used is UEP 3 (or EEP 3A for DAB+ services). Instead of using UEP 3 / EEP 3A, individual programme services on a multiplex can make their signals more robust by using either UEP 2 or UEP 1 (EEP 2A or EEP 1A for DAB+ services). However, using increased levels of error protection requires the use of additional amounts of data. In other words, if higher levels of error protection are used less data capacity remains available for other uses. Therefore, as the following table explains, using higher levels of error protection means that, because it has a finite and fixed data capacity, the overall multiplex is then only able to carry a smaller total number of programme services.
|
||
Data Rate Used /
Protection Level |
Capacity Units Used
(Per Programme Service) |
Maximum Nunber of
Services on Multiplex |
192 kbps / UEP 3 | 140 CU (DAB) | 06 = 840 CU (24 spare) |
192 kbps / UEP 2 | 168 CU (DAB) | 05 = 840 CU (24 spare) |
192 kbps / UEP 1 | 208 CU (DAB) | 04 = 832 CU (32 spare) |
160 kbps / UEP 3 | 116 CU (DAB) | 07 = 812 CU (52 spare) |
160 kbps / UEP 2 | 140 CU (DAB) | 06 = 840 CU (24 spare) |
160 kbps / UEP 1 | 168 CU (DAB) | 05 = 840 CU (24 spare) |
128 kbps / UEP 3 | 096 CU (DAB) | 09 = 864 CU (00 spare) |
128 kbps / UEP 2 | 116 CU (DAB) | 07 = 812 CU (52 spare) |
128 kbps / UEP 1 | 140 CU (DAB) | 06 = 840 CU (24 spare) |
112 kbps / UEP 3 | 084 CU (DAB) | 10 = 840 CU (24 spare) |
112 kbps / UEP 2 | 104 CU (DAB) | 08 = 832 CU (32 spare) |
112 kbps / UEP 1 | [Out of specification] | [Out of specification] |
096 kbps / UEP 3 | 070 CU (DAB) | 12 = 840 CU (24 spare) |
096 kbps / UEP 2 | 084 CU (DAB) | 10 = 840 CU (24 spare) |
096 kbps / UEP 1 | 104 CU (DAB) | 08 = 832 CU (32 spare) |
080 kbps / UEP 3 | 058 CU (DAB) | 12 = 840 CU (24 spare) |
080 kbps / UEP 2 | 070 CU (DAB) | 10 = 840 CU (24 spare) |
080 kbps / UEP 1 | 084 CU (DAB) | 08 = 832 CU (32 spare) |
064 kbps / UEP 3 | 048 CU (DAB) | 18 = 864 CU (00 spare) |
064 kbps / UEP 2 | 058 CU (DAB) | 14 = 812 CU (52 spare) |
064 kbps / UEP 1 | 070 CU (DAB) | 12 = 840 CU (24 spare) |
056 kbps / EEP 3A | 042 CU (DAB+) | 20 = 840 CU (24 spare) |
056 kbps / EEP 2A | 063 CU (DAB+) | 13 = 819 CU (44 spare) |
056 kbps / EEP 1A | 084 CU (DAB+) | 10 = 840 CU (24 spare) |
048 kbps / EEP 3A | 036 CU (DAB+) | 24 = 864 CU (00 spare) |
048 kbps / EEP 2A | 054 CU (DAB+) | 16 = 864 CU (00 spare) |
048 kbps / EEP 1A | 072 CU (DAB+) | 12 = 864 CU (00 spare) |
032 kbps / EEP 3A | 024 CU (DAB+) | 36 = 864 CU (00 spare) |
032 kbps / EEP 2A | 036 CU (DAB+) | 24 = 864 CU (00 spare) |
032 kbps / EEP 1A | 048 CU (DAB+) | 18 = 864 CU (00 spare) |
024 kbps / EEP 3A | 018 CU (DAB+) | 48 = 864 CU (00 spare) |
024 kbps / EEP 2A | 027 CU (DAB+) | 32 = 864 CU (00 spare) |
024 kbps / EEP 1A | 036 CU (DAB+) | 24 = 864 CU (00 spare) |
Note: Each line of the above table assumes that all the services listed in column 3 are operated at the same bit-rate and error-correction level as that detailed in column 1. | ||
|
|||
Programme Service Type (examples)
|
DAB
|
DAB+
|
Notes
|
Stereo Audio (“high” quality / music services) |
192 kbps (140 CU) |
80 kbps (60CU) |
UEP3 / EEP3A |
Stereo Audio (“good” quality / music services) |
128 kbps (96 CU) |
64 kbps (48 CU) |
UEP3 / EEP3A |
Stereo Audio (“standard” quality / music services) |
112 kbps (96 CU) |
48 kbps (36 CU) |
UEP3 / EEP3A |
Mono Audio (“good” quality / music services) |
96 kbps (70 CU) |
48 kbps (36 CU) |
UEP3 / EEP3A |
Mono Audio (music / speech services) |
64 kbps (48 CU) |
32 kbps (24 CU) |
UEP3 / EEP3A |
Public Service Announcements (e.g. weather, travel etc.) |
48 kbps (35 CU) |
24 kbps (18 CU) |
UEP3 / EEP3A |
NOTES:
The slight differences in the number of capacity units required for some bitrates using DAB or DAB+ can be accounted for by differences in block size. However, the key point is that the bit rate required for a given perceived degree of audio quality is substantially reduced. According to WorldDMB, the DAB+ standard “allows for up to three times as many services per multiplex” such that “[a] 40 kbps sub-channel with HE-AAC v2 provides a similar audio quality (even slightly better in most cases) as MPEG Audio Layer II at 128 kbps” (WorldDMB: 2012: 1).
The enhanced efficiency of the revised standard is reflected in the capacity requirements of receiver design specifications, for example, as set out by the UK government in its ‘Minimum Specifications For DAB & DAB+ In-Vehicle Digital Radio Receivers & Adaptors‘: A receiver must be able to decode a DAB audio service contained in a sub-channel of a size up to and including 280 Capacity Units (e.g. 256 kbps@UEP1)”. DAB audio services are defined in ETSI EN 300 401.A receiver must be able to decode a DAB+ audio service contained in a sub-channel of a size up to and including 144 Capacity Units (e.g. 96 kbps@EEP1A). DAB+ audio services are defined in ETSI TS 102 563 (DCMS: 2013: 13).
Bit Rate | DAB | DAB CU | DAB+ | DAB+CU |
---|---|---|---|---|
192 kbps | “High” quality stereo audio |
140 | Not used by FDN | 144 CU |
192 kbps: This is the maximum bitrate used for original DAB standard stereo programme services on the FDN Greater Norwich Multiplex. This bit rate cannot be used at higher protection levels (i.e. UEP 2 or UEP 1) because to do so would “break” the 140 Capacity Unit decoding limit of some older DAB receivers. | ||||
184 kbps | Out of specification | n/a | Not used by FDN | 138 CU |
176 kbps | Out of specification | n/a | Not used by FDN | 132 CU |
168 kbps | Out of specification | n/a | Not used by FDN | 126 CU |
160 kbps | “Very good” quality stereo audio |
116 CU | Not used by FDN | 120 CU |
160 kbps: This bitrate is used for original DAB standard stereo programme services on the FDN Greater Norwich Multiplex. Although this bit rate can be used at the higher protection level of UEP 2, it cannot be used at UEP 1, because to do so would “break” the 140 Capacity Unit decoding limit of some older DAB receivers. | ||||
152 kbps | Out of specification | n/a | Not used by FDN | 114 CU |
144 kbps | Out of specification | n/a | Not used by FDN | 108 CU |
136 kbps | Out of specification | n/a | Not used by FDN | 102 CU |
128 kbps | “Good” quality stereo audio< |
096 CU | Not used by FDN | 096 CU |
128 kbps: This is the “typical” bitrate used for original DAB standard stereo programme services on the FDN Greater Norwich Multiplex. This bit rate can also be used at the higher protection levels of UEP 2 and UEP 1. | ||||
120 kbps | Out of specification | n/a | Not used by FDN | 090 CU |
112 kbps | “Adequate” quality stereo audio |
084 CU | Not used by FDN | 084 CU |
112 kbps: This bitrate may be used for original DAB standard stereo programme services on the FDN Greater Norwich Multiplex. This bit rate can also be used at the higher protection levels of UEP 2 and UEP 1. | ||||
104 kbps | Out of specification | n/a | Not used by FDN | 078 CU |
096 kbps | “High” quality mono audio services |
70 CU | Not used by FDN | 072 CU |
096 kbps: This bitrate may be used for original DAB standard mono programme services on the FDN Greater Norwich Multiplex. This bit rate can also be used at the higher protection levels of UEP 2 and UEP 1. | ||||
088 kbps | Out of specification | n/a | Not used by FDN | 066 CU |
080 kbps | “Good” quality mono audio |
70 CU | Not used by FDN | 060 CU |
080 kbps: This bitrate may be used for original DAB standard mono programme services on the FDN Greater Norwich Multiplex. This bit rate can also be used at the higher protection levels of UEP 2 and UEP 1. | ||||
072 kbps | Out of specification | n/a | Not used by FDN | 054 CU | 064 kbps | “Adequate” quality mono audio |
48 CU | “Very high” quality stereo audio |
048 CU |
064 kbps: This bitrate may be used for original DAB standard mono programme services on the FDN Greater Norwich Multiplex. This bit rate can also be used at the higher protection levels of UEP 2 and UEP 1. | ||||
064 kbps: This bitrate may be used for DAB+ standard stereo programme services on the FDN Greater Norwich Multiplex. This bit rate can also be used at the higher protection levels of EEP 2A and EEP 1A. | ||||
056 kbps | Not used by FDN | 42 CU | “High” quality stereo audio |
042 CU |
056 kbps: This bitrate may be used for DAB+ standard stereo programme services on the FDN Greater Norwich Multiplex. This bit rate can also be used at the higher protection levels of EEP 2A and EEP 1A. | ||||
048 kbps | Not used by FDN | 35 CU | “Good” quality stereo audio |
036 CU |
048 kbps: This is the “typical” bitrate used for DAB+ standard stereo programme services on the FDN Greater Norwich Multiplex. This bit rate can also be used at the higher protection levels of EEP 2A and EEP 1A. | ||||
040 kbps | Out of specification | n/a | “Good” quality mono audio |
030 CU |
040 kbps: This bitrate may be used for DAB+ standard mono (or stereo) programme services on the FDN Greater Norwich Multiplex. This bit rate can also be used at the higher protection levels of EEP 2A and EEP 1A. | ||||
032 kbps | Not used by FDN | 24 CU | “Adequate” quality mono audio |
024 CU |
032 kbps: This bitrate is used for DAB+ standard mono programme services on the FDN Greater Norwich Multiplex. This bit rate can also be used at the higher protection levels of EEP 2A and EEP 1A. | ||||
024 kbps | Out of specificationN | n/a | “communcations” quality mono audio |
018 CU |
024 kbps: This bitrate is available for information service (weather, travel etc.) type DAB+ standard mono programme services on the FDN Greater Norwich Multiplex. This bit rate can also be used at the higher protection levels of EEP 2A and EEP 1A. | ||||
016 kbps | Out of specification | n/a | Not used by FDN | 014 CU |
012 kbps | Out of specification | n/a | Not used by FDN | 009 CU |
008 kbps | Out of specification | n/a | Not used by FDN | 006 CU |