Alan Hughes takes a look at the changes in DAB+ Data Rates
ABC/SBS Data Rates
By the 18th June the ABC/SBS DAB+ digital radio signal quality will have been modified.
ABC Classic has been increased from 80 kbit/s to 120 kbit/s. After all the initial sound quality complaints, many of which were unjustified, it will be interesting to see if anyone notices.
ABC Jazz has been increased slightly to 88 kbit/s, which is not likely to make a noticeable difference.
The losers are been ABC country, triple j and triple j Unearthed which are reduced from 80 kbit/s to 72 kbit/s. This is interesting because triple j’s younger audience should have better hearing.
ABC Kids Listen has also been reduced from 72 to 64 kbit/s.
The ABC local radio for each capital city is still transmitted in 64 kbit/s which has changed from dual channel to parametric stereo, despite their AM transmitter radiating in mono with the exception of Darwin, which is in FM stereo.
SBS is unchanged, meaning that their Chill and Pop Asia are still 72 kbit/s stereo. For ABC and SBS speech only programs 40 kbit/s is used.
Community broadcasters are mostly 48 or 64 kbit/s.
Commercial radio Data Rates in general has gone for quantity of different programs compared to quality.
Southern Cross Austereo has made all of their many programs 32 kbit/s using parametric stereo.
Parametric Stereo can be likened to FM Stereo Encoding where a Mono signal is transmitted, but also a bit of extra info is sent to make up the stereo information (L+R, L-R in FM terms). The other national networks as well as 6IX are 48 kbit/s stereo each.
The cost of Broadcasting
A single ABC/SBS DAB+ transmitter carries 18 programs. The commercial/ community DAB+ transmitters are carrying up to 32 programs each, makes it the cheapest and least polluting means of moving sound from a microphone to the listeners speaker.
Streaming through the mobile phone and NBN networks means that each listener will have to be provided with their own signal, much more expensive and polluting. If broadcast transmitters were not used, there would have to be many more transceivers in mobile phone towers, which will require more spectrum to be purchased from the ACMA.
The telcos will charge listeners all listeners for this through increased prices. The NBN will also need more fibre optic links between telephone exchanges and the broadcasters.
How to reduce the cost of regional broadcasting
For country areas there is band 1 DRM which covers a much bigger area than DAB+ and a larger area than FM. A single DRM transmitter can carry both commercial programs in better quality than now.
There is data capacity for slideshow advertising, an indexed text service including pictures called Journaline.
This will reduce transmission costs particularly for those with an AM transmitter. The ABC/SBS can also use band 1 DRM to carry all their 18 programs using 6 channels on a single transmitter in each country area. There is an emergency warning functionality, for those in an emergency area can wake the radio, tune it to the emergency channel, wake potential victims and give an announcement. It can also show maps and detailed instructions as well as redirect vehicle navigation systems around police closed roads.
DAB+ has only 8 transmission channels available in Australia, the rest are used by television, whereas there are 206 band 1 DRM. This means that there are enough channels to install DRM on existing FM transmitter towers.
There are now single chip digital receivers which will receive DAB+ and DRM on the market overseas.
About the Author
Alan Hughes is a technical author who has taught broadcast technologists for 20 years.