Raspberry Pi Generates DAB+ Multiplex Stream
The network has run for more than two months and has proven to be very reliable
September 25, 2017
EINDHOVEN, the Netherlands — A small-scale DAB broadcasting project in Eindhoven, the Netherlands, has successfully tested an extremely low cost contribution chain for DAB+ multiplexes. The scalable architecture “might well be the most cost effective solution to date for local broadcasters interested in DAB transmissions to create a DAB multiplex stream,” according to WorldDAB.org.
As part of the DAB+ 4 Brainport project, it was decided to apply the well-known Open Digital Radio software on low-cost Raspberry Pi processing units. With these, a contribution network was built, transferring the signals from 7 local radio stations to a central multiplex unit, which then supplies the multiplex stream to the DAB distribution network. The network has run for more than two months and has proven to be very reliable. (Any service interruptions that occurred ultimately turned out to be due to unannounced changes in the provisioning of the audio streams or other problems in the delivery of the audio source. None were due to problems with the Raspberry Pi units or the programs applied.) “Contrary to a number of DAB experiments currently run in the Netherlands I wanted to test whether or not low cost distributed processing could provide a reliable DAB multiplex stream for our local DAB network,” said Gerard Lokhoff, the initiator of the DAB+ 4 Brainport project. “I'm very satisfied with the result, proving that such small scale projects can provide valuable options for local broadcasters.”
The architecture allows for a hybrid structure, in which radio stations can either encode the audio in-house, which also enables them to easily change the text (DLS) or image (MOT) information embedded in the audio stream, or use a central audio encoder at the multiplex site. The processing power of the Raspberry Pi is enough to encode up to four radio stations on a single unit simultaneously, with the limiting factor actually being the temperature of the processing core. The final multiplexing of the signals requires very little processing power. The cost of this DAB contribution chain set up nicely scales with the number of different Raspberry Pi units used: If every radio station decides to encode the audio in-house, it will cost about €50–60 per station (US $60– $71) plus €50–60 for the multiplexing unit. Reliable Internet connections must be available, with enough bandwidth to support the encoded audio streams (typically about 64 to 128 kbits/sec per station) as well as the DAB multiplex signal (max 2 Mbps).
More detailed information on this low-cost DAB methodology can be found here: https://github.com/glokhoff/RaspDAB/wiki