First licensed open dab transmission
Contents |
Performance
For the first time, the open source encoder, multiplexer, modulator designed by CRC (MMBTools) has been used for a licensed local transmission during Label Suisse festival for a performance done together with MXLabs.
Swiss Administration has granted a 8 channels DAB multiplex to be used on air on channel 10A during the festival between 17th to 19th September 2010 in Lausanne.
The installation consisted of a single PC running Linux and with a 8 channels soundcard and USRP doing the DAB encoding, multiplexing and modulation. This transmission transmitted in DAB the audio of a mosaic of 8 music bands that were video projected for the performance. DAB Radios tuned to all these channels were hanging from the ceiling and people were also able to receive the signal in the station and surroundings.
It is already a long time that people are experimenting DAB transmission using CRC MMBTools and Open Software Defined Radio but it is is the first time it is used for a licensed transmission. This milestone demonstrate that digital radio has become democratized not only for experimentation but also for local or ultra-local transmission.
The installation consist of a recent AMD PC and a USRP Generic Software Radio Platform for the transmission. The software tools ar CRC MMBtools with custom linux scripts and python code.
For more information: Mathias Coinchon (broadcast at opendigitalradio.org) or Stanislas Roehrich (http://www.maxxima.org).
Links:
Setup
Pre-requisites
Hardware:
- dualcore AMD PC running (ubuntu) linux
- M audio delta 1010 soundcard
- USRP1 Universal Software Radio Peripheral
- Mini-circuits bandpass filter
Software:
- Jack open Audio connection kit
- arecord (from ALSA utils)
- Toolame open MPEG Layer II encoder
- CRC MMBtools open source DAB multiplexer: CRC-DabMux
- Non blocking buffer: bfr
- CRC MMBtools open source DAM modulator: CRC-DabMod
- Baseband USRP1 VHF player
Scripts
2 scripts were used, one for the multiplexer/modulator and the other for getting the sound stream and encode them
Stream and encode (example with 3 programs, definite script to be posted):
#!/bin/sh arecord -t raw -f S16_LE -c 2 -r 48000 -D jackplug1 |toolame -s 48 -D 4 -b 128 /dev/stdin ./1.ff & arecord -t raw -f S16_LE -c 2 -r 48000 -D jackplug2 |toolame -s 48 -D 4 -b 128 /dev/stdin ./2.ff & arecord -t raw -f S16_LE -c 2 -r 48000 -D jackplug3 |toolame -s 48 -D 4 -b 128 /dev/stdin ./3.ff &
.ff are FIFO files (names pipes) that were created using "mkfifo" command
Multiplexing, encoding, playout (example with 3 program, definite script to be posted)
CRC-DabMux -L "LabelSuisse" -A 1.ff -b 128 -i 1 -S -L "Label1" -C \ -A 2.ff -b 128 -i 2 -S -L "Label2" -C \ -A 3.ff -b 128 -i 3 -S -L "Label3" -C \ -O fifo:///dev/stdout |\ CRC-DabMod -f -g1 -r3200000 |\ bfr -p -b 32m -m 8m |\ coinwap_full3.py
(bfr is the buffer, coinwap_full3.py is the baseband player)
Event Pictures and video
Video of the performance:
Radio Mount for the Ceiling
Fixing the Screen
Dab Mux test, 8 Live Audio Channels from the Delta1010
Video Mosaïc
Dab Mux In A box !
Radio Tuning ;)
Audio Triming... lipsync
DAB enc/mux/mod in a box
Content of the black box (pics by Stefan Heimers)
Working finally !
Conclusion
We could demonstrate that a local DAB multiplex can be made at very little cost using open source technologies.
However we discovered problems that need to be solved. The USRP was regularly freezing requiring the scripts to be relaunched. We have not been able to reproduce this problem in the lab but the origin is certainly a power supply problem in the presence of a dirty AC power distribution (as it is commonly found in festivals). We suspect also high heat in the box to be the cause of these unstabilities. For this reason, we will change the USRP power supply and improve the cooling of USRP (with heatsinks and better fan).
See also:
