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DSDcc

DSDcc is a complete rewrite from the original DSD (Digital Speech Decoder) project.

It is rewritten along the following lines:

  • A purely C++ library with a single decoder object at its central point
  • Works by pushing new samples to the decoder at the upper level rather than pulling it from the underlying filesystem (actual file or device) at the lowest level. This facilitates integration with software using it as a true library. This comes especially handy for projects in Qt that cannot afford using pthreads on their own like gr-dsd does. In fact the main drive for this is to integrate it in a plugin of SDRangel.
  • Works by polling to get possible new MBE or audio samples after new samples have been pushed to the decoder
  • Option to output audio samples as L+R (stereo) samples with L=R as this may facilitate integration
  • A binary that uses this library is provided for integration with other commands that run in a shell. So basically it works only with input / output files possibly being stdin / stdout to be integrated in a pipe command. There is no direct usage of audio devices nor fancy side reading from or writing to .wav or .mbe files.
  • mbelib usage is optional at compile time. Without mbelib only the raw MBE samples can be extracted to be processed outside of DSDcc with the help of a hardware dongle for example thus lifting the possible copyright violations (See next)

These points have been retained from the original:

  • The decoding methods
  • Minimal changes to the options and state structures
  • Input as S16LE samples at a fixed rate of 48kS/s
  • Audio output as S16LE samples at 8kS/s rate directly out of mbelib or upsampled to 48kS/s

Possible copyright issues with mbelib

While DSDcc is intended to be patent-free, mbelib that it uses describes functions that may be covered by one or more U.S. patents owned by DVSI Inc. The source code itself should not be infringing as it merely describes possible methods of implementation. Compiling or using mbelib may infringe on patents rights in your jurisdiction and/or require licensing. It is unknown if DVSI will sell licenses for software that uses mbelib.

If you are not comfortable with this just do not compile with mbelib support and you will still be able to extract the MBE frames and process them outside DSDcc with the help of a hardware dongle for example (e.g. ThumbDV USB dongle). The provided binary dsdccx can use such a dongle with SerialDV. See the Building section for details.

If you still want mbelib support you have to use the -DUSE_MBELIB=ON directive on the cmake command line and of course you need to have mbelib installed in your system.

Supported formats

These are a subset of the ones covered by the original DSD project plus other formats. A large part of the code was rewritten more noticeably the symbol timing and the DMR processing improving a lot from the original DSD. For now we have:

  • DMR/MOTOTRBO: ETSI two slot TDMA standard. MOTOTRBO is a popular implementation of this standard.
  • D-Star: developed and promoted by Icom for Amateur Radio customers.
  • dPMR: ETSI narrowband FDMA standard. This is somehow similar to NXDN 2400 Baud rate mode.
  • Yaesu System Fusion (abbreviated YSF): developed and promoted by Yaesu for Amateur Radio customers partly inspired by gr-ysf. Voice full rate with SerialDV is not supported.

Next we may like to add NXDN exploiting similarities with the already implemented dPMR.

Source code

Repository branches

  • master: the production branch
  • dev: the development branch

Building

As usual with projects based on cmake create a build directory at the root of the cloned repository and cd into it.

For mbelibsupport you will need to specify the -DUSE_MBELIB=ON directive on the cmake command line and you will need to have mbelib installed in your system. If you use custom installation paths like /opt/install/mbelib for example you will need to add the include and library locations to the cmake command line with these directives: -DLIBMBE_INCLUDE_DIR=/opt/install/mbelib/include -DLIBMBE_LIBRARY=/opt/install/mbelib/lib/libmbe.so

For DVSI AMBE3000 serial device support (e.g. ThumbDV) in the binary dsdccx you will need to install SerialDV. Please refer to the Readme.md in this package to install SerialDV. If you have SerialDV installed in a custom directory say /opt/install/serialdv you will need to add the include and library locations to the cmake command line with these directives: -DLIBSERIALDV_INCLUDE_DIR=/opt/install/serialdv/include/serialdv -DLIBSERIALDV_LIBRARY=/opt/install/serialdv/lib/libserialdv.so

So the full cmake command with a custom installation directory and mbelibsupport will look like: cmake -Wno-dev -DCMAKE_INSTALL_PREFIX=/opt/install/dsdcc -DUSE_MBELIB=ON -DLIBMBE_INCLUDE_DIR=/opt/install/mbelib/include -DLIBMBE_LIBRARY=/opt/install/mbelib/lib/libmbe.so ..

The full cmake command with a custom installation directory no mbelibsupport and SerialDV support for the binary will look like: cmake -Wno-dev -DCMAKE_INSTALL_PREFIX=/opt/install/dsdcc -DLIBSERIALDV_INCLUDE_DIR=/opt/install/serialdv/include/serialdv -DLIBSERIALDV_LIBRARY=/opt/install/serialdv/lib/libserialdv.so

Then:

  • make or make -j8 on a 8 CPU machine
  • make install

Running

A binary dsdccx is produced and gets installed in the bin subdirectory of your installation directory. A typical usage is to pipe in the input from a UDP source of discriminator output samples with socat and pipe out to sox play utility to produce some sound: socat stdout udp-listen:9999 | /opt/install/dsdcc/bin/dsdccx -i - -fa -o - | play -q -t s16 -r 8k -c 1 -

You can also run the example files in the samples directory. Please refer to the readme in this directory for instructions.

For more details refer to the online help with the -h option: dsdccx -h

Since version 1.6 dsdccx has the capability of sending regularly the traffic status messages to a file using the -M option. See messagefile.md for details.


(For use with serialDV) Since kernel 4.4.52 the default for FTDI devices (that is in the ftdi_sio kernel module) is not to set it as low latency. This results in the ThumbDV dongle not working anymore because its response is too slow to sustain the normal AMBE packets flow. The solution is to force low latency by changing the variable for your device (ex: /dev/ttyUSB0) as follows:

echo 1 | sudo tee /sys/bus/usb-serial/devices/ttyUSB0/latency_timer or sudo setserial /dev/ttyUSB0 low_latency


Developpers notes

Structure overview

  • Everything lives in the DSDcc namespace
  • The DSDDecoder object handles the core functions of synchronization and global orchestration of the decoding. It also hosts the options and state objects. It collaborates with specialized objects that have full access to the decoder public and private areas using the C++ friend directive.
  • The options and state objects are the following:
    • The DSDOpts object handles the options configuring the behaviour of the decoder
    • The DSDState object handles the run time data and data related to the current state of the decoder
  • The DSDSymbol object is responsible for symbol and dibit processing. It receives a new sample with its pushSample() method. It processes it and when enough samples have been receives it can produce a new symbol that it stores internally.
  • The DSDMBEDecoder object is responsible of taking in AMBE frames and producing the final audio output at 8 kS/s. It is a wrapper around the mbelib library. It also handles the optional upsampling of audio to 48 kS/s.
  • The objects specialized in the decoding of the various formats are:
    • The DSDDMR object is responsible of handling the processing of DMR frames. It uses the service of DSDMBEDecoder to produce the final audio output.
    • The DSDdPMR object is responsible of handling the processing of dPMR frames. It uses the service of DSDMBEDecoder to produce the final audio output.
    • The DSDDstar object is responsible of handling the processing of D-Star frames. It uses the service of DSDMBEDecoder to produce the final audio output.
    • The DSDYSF object is responsible of handling the processing of Yaesu System Fusion frames. It uses the service of DSDMBEDecoder to produce the final audio output.
  • Some utility objects are also defined:
    • The Descramble object contains static data and methods mainly used in the decoding of D-Star frames. It is based on Jonathan Naylor G4KLX code.
    • The DSDFilters object as the name implies contains methods to perform various forms of DSP filtering.

Typical integration

You can look at the source of the dsdccx binary to get an idea. Basically it involves the following steps:

  1. Allocate a new DSDDecoder object (stack or heap)
  2. Set the options and state object. with some DSDDecoder methods.
  3. Prepare the input (open file or stream)
  4. Get a new sample from the stream
  5. Push this sample to the decoder
  6. With mbelib support: a. Check if any audio output is available and possibly get its pointer and number of samples b. Push these samples to the audio device or the output file or stream
  7. With a DVSI AMBE3000 based serial device and SerialDV support: a. use DSDcc::DVController helper class with the processDVSerial method b. Check if any audio output is available from the helper class and possibly get its pointer and number of samples c. Push these samples to the audio device or the output file or stream
  8. Go back to step #5 until a signal is received or some sort of logic brings the loop to an end
  9. Do the cleanup after the loop or in the signal handler (close file, destroy objects...)

Of course this loop can be run in its own thread or remain synchronous with the calling application. Unlike with the original DSD you have the choice.

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Digital Speech Decoder (DSD) rewritten as a C++ library

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