Codec 2 is an open source (LGPL 2.1) low bit rate speech codec:

http://rowetel.com/codec2.html

Also included:

• FreeDV API source code. FreeDV is an open source digital voice protocol that integrates the modems, codecs, and FEC
• FDMDV DPSK modem (README_fdmdv) for HF channels
• Coherent PSK ((README_cohpsk) for HF channels
• Non-coherent FSK modem (README_fsk)
• Coherent OFDM modem for HF channels (README_ofdm)
• software for High Altitude Balloon image and telemetry reception

Also see INSTALL for more general building and installing instructions.

1/ Listen to Codec 2:

$ cd codec2
$ mkdir build_linux
$ cd build_linux
$ cmake ..
$ make
$ ./src/c2demo ../raw/hts1a.raw hts1a_c2.raw
$ play -t raw -r 8000 -e signed-integer -b 16 ../raw/hts1a.raw
$ play -t raw -r 8000 -e signed-integer -b 16 ./hts1a_c2.raw

2/ Compress, decompress and then play a file:

using 2400 bps bit rate encoding

$ ./src/c2enc 2400 ../raw/hts1a.raw hts1a_c2.bit
$ ./src/c2dec 2400 hts1a_c2.bit hts1a_c2_2400.raw 

which can be played with

$ play -t raw -r 8000 -e signed-integer -b 16 ./hts1a_c2_2400.raw

using 700C bps bit rate encoding

$ ./src/c2enc 700C ../raw/hts1a.raw hts1a_c2.bit
$ ./src/c2dec 700C hts1a_c2.bit hts1a_c2_700.raw

which can be played with

$ play -t raw -r 8000 -e signed-integer -b 16 ./hts1a_c2_700.raw

3/ Same thing with pipes:

$ ./src/c2enc 1300 ../raw/hts1a.raw - | ./src/c2dec 1300 - - | play -t raw -r 8000 -s -2 -

• c2demo encodes a file of speech samples, then decodes them and saves the result.

• c2enc encodes a file of speech samples to a compressed file of encoded bits. c2dec decodes a compressed file of bits to a file of speech samples.

• c2sim is a simulation/development version of Codec 2. It allows selective use of the various Codec 2 algorithms. For example switching phase modelling or LSP quantisation on and off.

• freedv_tx/freedv_rx are command line implementations of the FreeDV protocol, which combines Codec 2, modems, and Forward Error Correction (FEC).

• cohpsk_* are coherent PSK (COHPSK) HF modem command line programs.

• drs232, drs232_ldpc, and horus_demod are used for receiving images and telemetry from high altitude balloons (Project Horus Wenet, Horus Binary protocol)

• fdmdv_* are differential PSK HF modem command line programs (README_fdmdv).

• fsk_* are command line programs for a non-coherent FSK modem (README_fsk).

• ldpc_* are LDPC encoder/decoder command line programs, based on the CML library.

• ofdm_* are OFDM PSK HF modem command line programs (README_ofdm).

NOTE: Instructions assume you are creating a build_linux directory from within the source directory. Adjust paths as needed if this is not the case.

1. Build codec2 initially without LPCNet

   $ cd ~
   $ git clone https://github.com/drowe67/codec2.git
   $ cd codec2 && mkdir build_linux && cd build_linux
   $ cmake ../
   $ make
   

2. Build LPCNet:

   $ cd ~
   $ git clone https://github.com/drowe67/LPCNet
   $ cd LPCNet && mkdir build_linux && cd build_linux
   $ cmake -DCODEC2_BUILD_DIR=~/codec2/build_linux ../ 
   $ make
   

3. (Re)build Codec 2 with LPCNet support:

   $ cd ~/codec2/build_linux && rm -Rf *
   $ cmake -DLPCNET_BUILD_DIR=~/LPCNet/build_linux ..
   $ make
   

Reference: Plugging together lpcnet_enc -> ofdm_mod -> ofdm_demod -> lpcnet_dec:

$ cat ~/LPCNet/wav/wia.wav | ~/LPCNet/build_linux/src/lpcnet_enc -s | ./ofdm_mod --nc 31 --ldpc 2 --verbose 1 -p 312 | ./ofdm_demod --nc 31 --verbose 1 --ldpc 2 -p 312 | ~/LPCNet/build_linux/src/lpcnet_dec -s | aplay -f S16_LE -r 16000

We are trying to integrate all of the above into FreeDV API.

Listen the reference tx:

$ cat ~/LPCNet/wav/wia.wav | ~/LPCNet/build_linux/src/lpcnet_enc -s | ./ofdm_mod --nc 31 --ldpc 2 --verbose 1 -p 312 | aplay -f S16_LE

Listen the freedv_tx:

$ ./freedv_tx 2020 ~/LPCNet/wav/wia.wav - | aplay -f S16_LE

FreeDV API tx, with reference rx from above:

$ ./freedv_tx 2020 ~/LPCNet/wav/wia.wav - | ./ofdm_demod --nc 31 --verbose 1 --ldpc 2 -p 312 | ~/LPCNet/build_linux/src/lpcnet_dec -s | aplay -f S16_LE -r 16000

FreeDV API tx and rx:

$ ./freedv_tx 2020 ~/Downloads/wianews-2019-01-20.s16 - | ./freedv_rx 2020 - - | aplay -f S16_LE -r 16000
$ ./freedv_tx 2020 ~/Downloads/wianews-2019-01-20.s16 - --testframes | ./freedv_rx 2020 - /dev/null --testframes -vv

Simulated HF slow fading channel, 10.8dB SNR:

$ ./freedv_tx 2020 ~/LPCNet/wav/all.wav - | ./cohpsk_ch - - -30 --Fs 8000 --slow | ./freedv_rx 2020 - - | aplay -f S16_LE -r 16000

It falls down quite a bit with fast fading (--fast). We'll work on that.

AWGN (noise but no fading) channel, 2.8dB SNR:

$ ./freedv_tx 2020 ~/LPCNet/wav/all.wav - | ./cohpsk_ch - - -22 --Fs 8000 | ./freedv_rx 2020 - - | aplay -f S16_LE -r 16000

CTest is used as a test frame work, with support from GNU Octave scripts.

1/ Install GNU Octave on Ubuntu with:

$ sudo apt install octave octave-control octave-parallel octave-signal octave-specfun

(see also Octave section below)

2/ To build and run the tests:

$ cd ~/codec2
$ rm -Rf build_linux && mkdir build_linux
$ cd build_linux
$ cmake -DCMAKE_BUILD_TYPE=Debug ..
$ make all test

3/ To just run tests without rebuilding:

$ make test

4/ To get a verbose run (e.g. for test debugging):

$ ctest -V

5/ To just run a single test:

$ ctest -R test_OFDM_modem_octave_port

5/ To list the available tests:

$ ctest -N

cmake       - cmake support files
misc        - misc C programs that have been useful in development,
              not reqd for Codec 2 release. Part of Debug build.
octave      - Octave scripts used to support development
script      - shell scripts for playing and converting raw files
src         - C source code for Codec 2, FDMDV modem, COHPSK modem, FreeDV API
raw         - speech files in raw format (16 bits signed linear 8 kHz)
stm32       - STM32F4 microcontroller and SM1000 FreeDV Adaptor support
unittest    - Code to perform and support testing. Part of Debug build.
wav         - speech files in wave file format

1/ To compile with debug symbols for using gdb:

$ cd ~/codec2
$ rm -Rf build_linux && mkdir build_linux
$ cd build_linux
$ CFLAGS=-g cmake ..
$ make

2/ For dump file support (dump data from c2sim for input to Octave development scripts):

$ cd ~/codec2
$ rm -Rf build_linux && mkdir build_linux
$ cd build_linux
$ CFLAGS=-DDUMP cmake ..
$ make

On Ubuntu 17:

$ sudo apt-get install mingw-w64
$ mkdir build_windows && cd build_windows
$ cmake .. -DCMAKE_TOOLCHAIN_FILE=/home/david/freedv-dev/cmake/Toolchain-Ubuntu-mingw32.cmake -DUNITTEST=FALSE -DGENERATE_CODEBOOK=/home/david/codec2/build_linux/src/generate_codebook 
$ make

mkdir build_windows (Or what ever you want to call your build dir) cmake -G "MinGW Makefiles" -D CMAKE_MAKE_PROGRAM=mingw32-make.exe Or if you use ninja for building cmake -G "Ninja" .. mingw32-make or ninja depends on what you used in the last command wait for it to build.

To run the Octave scripts the following libraries are required:

These can be installed using your systems package management system or the Octave package management system. The version number of each package is not important.

On Ubuntu install with:

$ sudo apt install octave octave-control octave-parallel octave-signal octave-specfun

See freedv_api.h and freedv_api.c, and the demo programs freedv_tx & freedv_rx. Quickstart demo using FreeDV 1600:

$ ./freedv_tx 1600 ../../raw/hts1.raw - | ./freedv_rx 1600 - - | play -t raw -r 8000 -s -2 -q -
$ cat freedv_rx_log.txt

FreeDV 2400A and FreeDV 2400B are modes designed for VHF radio. FreeDV 2400A is designed for SDR radios (it has a 5 kHz RF bandwidth), however FreeDV 2400B is designed to pass through commodity FM radios.

Demos of FreeDV 2400A and 2400B:

$ ./freedv_tx 2400A ../../raw/ve9qrp_10s.raw - | ./freedv_rx 2400A - - | play -t raw -r 8000 -s -2 -
$ ./freedv_tx 2400B ../../raw/ve9qrp_10s.raw - | ./freedv_rx 2400B - - | play -t raw -r 8000 -s -2 -

Note for FreeDV 2400A/2400B the modem signal sample rate is 48kHz. To listen to the modem tones from FreeDV 2400B, or play them into a FM HT mic input:

$ ./freedv_tx 2400B ../../raw/ve9qrp_10s.raw - | play -t raw -r 48000 -s -2 -

Simulate FreeDV 2400B passing through a 300 to 3000 Hz audio path using sox to filter:

$  ./freedv_tx 2400B ../../raw/ve9qrp_10s.raw - | sox -t raw -r 48000 -s -2 - -t raw - sinc 300-3000 | ./freedv_rx 2400B - - | play -t raw -r 8000 -s -2 -

• FreeDV 2400A blog post ...: http://www.rowetel.com/?p=5119
• FreeDV 2400A & 2400B demos: http://www.rowetel.com/?p=5219