Does anyone know the protocol compatibility with regard to DAB and Low Delay AAC codecs? Is AAC-LD data or AAC-ELD data compatible with AAC and AAC+ decoding. Or how likely is it that an AAC/AAC+ decoder would have built-in compatibility for the Low Delay codecs?

The simpler question behind the question: Is it possible to use DAB+ to broadcast audio without the latency of the traditional AAC+ codec?

  • $\begingroup$ Is the CODEC latency that relevant? as the DAB system has a multiplexer time offset (TIST) which can be of the order of Seconds if a satellite link is involved in ETI distribution. Frank $\endgroup$ – Frank Johnson Jun 30 '17 at 10:19
  • $\begingroup$ This should really be in the comments section. But are you suggesting that it is impossible to create a local broadcast of DAB+ (in the same manner of broadcasting FM) where there are many possible low latency applications $\endgroup$ – NewEndian Jul 3 '17 at 2:13

I'd say the average DAB+ receiver is unlikely to support AAC-LD or AAC-ELD, because AAC used in DAB+ (optionally with SBR and PS) uses a 960 granule length, unlike most AAC used elsewhere, which uses 1024. I don't know if ELD or LD exist for this granule length. The AAC codec is used in superframe-mode, with 120ms frame duration.

Regarding delay in general in a DAB transmission chain:

  • Some latency also comes from the time interleaver (see ETSI EN 300 401 v2.1.1 Clause 12)

  • In transmission mode I (the only one used since v2), one transmission frame lasts 96ms, also adding to the end-to-end latency

  • As @frank-johnson also mentioned, the distribution network sending ETI to all modulators of the transmitter network can also add several seconds of delay.

DAB wasn't designed for low-delay applications, and the latency of the codec only makes up a small part of the overall end-to-end delay.

If you want to experiment with generating DAB signals, have a look at http://www.opendigitalradio.org.


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