Codec2

Codec 2 is a low-bitrate speech audio codec (speech coding) that is patent free and open source. Codec 2 compresses speech using sinusoidal coding, a method specialized for human speech. Bit rates of 3200 to 450 bit/s have been successfully created. Codec 2 was designed to be used for amateur radio and other high compression voice applications. Codec 2 is a low-bitrate speech audio codec (speech coding) that is patent free and open source. Codec 2 compresses speech using sinusoidal coding, a method specialized for human speech. Bit rates of 3200 to 450 bit/s have been successfully created. Codec 2 was designed to be used for amateur radio and other high compression voice applications. The codec was developed by David Rowe, with support and cooperation of other researchers (e.g., Jean-Marc Valin from Opus). Codec 2 consists of 3200, 2400, 1600, 1400, 1300, 1200, 700 and 450 bit/s codec modes. It outperforms most other low-bitrate speech codecs. For example, it uses half the bandwidth of Advanced Multi-Band Excitation to encode speech with similar quality. The speech codec uses 16-bit PCM sampled audio, and outputs packed digital bytes. When sent packed digital bytes, it outputs PCM sampled audio. The audio sample rate is fixed at 8 kHz. The reference implementation is open source and is freely available in a subversion (SVN) repository. The source code is released under the terms of version 2.1 of the GNU Lesser General Public License (LGPL). It is programmed in C and so far doesn't work without floating-point arithmetic, although the algorithm itself does not require this. The reference software package also includes a frequency-division multiplex digital voice (FDMDV) software modem and a graphical user interface based on FLTK. The software is developed on Linux and a port for Microsoft Windows created with Cygwin is offered in addition to a Linux version. The codec has been presented in various conferences and has received the 2012 ARRL Technical Innovation Award, and the Linux Australia Conference's Best Presentation Award. Rowe has also created a frequency-division multiplex (FDM) modem which carries the digital voice (DV) in only 1.3 kHz of radio bandwidth. The codec and FDM modem are used every day on amateur radio shortwave bands using both the SM1000 hardware implementation, and the FreeDV application.