diff options
Diffstat (limited to 'scenarios.tex')
| -rw-r--r-- | scenarios.tex | 62 |
1 files changed, 51 insertions, 11 deletions
diff --git a/scenarios.tex b/scenarios.tex index d452f99..46fba1a 100644 --- a/scenarios.tex +++ b/scenarios.tex @@ -221,8 +221,29 @@ hackrf_transfer -t /tmp/ofdm.fifo -f 216928000 -x 47 \ \subsection{Audio Sources} Preparing a DAB multiplex with different programmes requires that we are able to -read and encode several audio sources. This audio data can reach the multiplexer -in different ways. We will go over different possibilities in this part. +read and encode several audio sources. We have seen in +section~\ref{sec:between_encoder_and_multiplexer} how the encoders can be +interfaced to the modulator. In this section we'll go through the different ways +to carry the audio data to the encoder. + +\subsubsection{Local Audio Card} +It is possible to use an audio card connected to the computer as source. For +very simple scenarios, the ALSA input for FDK-AAC-DABplus is easiest to set up. +This however limits the usage of a single encoder per sound-card, and will not +scale well if more than one programme has to be encoded on the machine. It is +however ideal for dedicated encoding machines that can contribute the encoded +audio over an IP network. + +An alternative to using ALSA is JACK\footnote{The JACK Audio Connection Kit is a + virtual audio patch, \url{http://www.jack-audio.org}} +that can be used with a multi-channel sound card. JACK will expose every audio +input channel, and several encoders can be launched that also connect to JACK. +The input channels can be freely connected to the encoders thanks to the virtual +JACK patch panel. + +\sidenote{It might be possible to use the libVLC input too, to be defined.} +FDK-AAC-DABplus supports JACK and ALSA input, but Toolame-dab supports only the +JACK input. \subsubsection{Using Existing Web-Streams} One common scenario is to transmit radio stations that already are available as @@ -240,18 +261,37 @@ is most often $48000\Hz$ or sometimes $32000\Hz$. A sample-rate conversion is necessary in the stream decoder. There are many different stream decoders, and gstreamer, mpg123 and mplayer have -been tested. We have achieved good results with mplayer, and the dab-scripts +been tested. By far the easiest way is to use the libVLC binding that can be +compiled for Toolame-dab and FDK-AAC-DABplus. This library has +the same features as the VLC audio player, but the audio data is directly passed +to the encoding routines. This allows the encoder to receive all network +sources VLC supports, not only HTTP web-streams but also less common setups +e.g.\ encoded audio inside multicast UDP MPEG-TS. +This is illustrated in ``Studio A'' in figure~\ref{fig:txchain-with-encoders}. + +We have also achieved good results with mplayer, and the dab-scripts repository\footnote{\url{http://github.com/Opendigitalradio/dab-scripts}} -contain the script \texttt{encode-jack.sh} that uses mplayer, and illustrates -how it is possible to encode a web-stream to \dabplus. JACK\footnote{The JACK - Audio Connection Kit is a virtual audio patch, -\url{http://www.jack-audio.org}} is used to interconnect the stream decoder to -the \dabplus encoder. +contains the script \texttt{encode-jack.sh} that uses mplayer, and illustrates +how it is possible to encode a web-stream to \dabplus. JACK is used to +interconnect the stream decoder to the \dabplus encoder. +This is illustrated in ``Studio B''. -This script is designed for production use, and also contains automatic restart -logic in case of a failure. +\begin{figure}[h] + \includegraphics[width=\textwidth]{figures/txchain-with-encoders.pdf} + \caption{Three common ways to encode a remote audio sources.} + \label{fig:txchain-with-encoders} +\end{figure} + + +The scripts are designed for production use, and also contain automatic restart +logic in case of a failure. They send an email and write a message into the +system log. \subsubsection{Encoders at Programme Originator Studios} -\subsubsection{Multi-capture Audio Card} +In order to avoid the unavoidable encoder cascading when using mp3 web-streams, +the DAB or \dabplus encoder has to be moved to the programme originator's +premises, and should directly encode the audio signal coming from the studios. +This is illustrated in ``Studio C'' in figure~\ref{fig:txchain-with-encoders}. + \subsection{Single-Frequency Networks} |