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codec 2 wikipedia jump to content main menu main menu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 overview 2 technology 3 adoption 4 history 5 references 6 external links toggle the table of contents codec 2 3 languages dansk deutsch polski edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia low bitrate speech encoding format codec 2 developer david grant rowe release august 25 2010 2010 08 25 stable release 1 2 0 june 24 2023 3 years ago 2023 06 24 written in c99 platform cross platform type audio codec license gnu lgpl v2 1 website www rowetel com page _id 452 repository github com drowe67 codec2 codec 2 is a low bitrate speech audio codec speech coding that is patent free and open source 1 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 overview edit the codec was developed by david grant rowe with support and cooperation of other researchers e g jean marc valin from opus 2 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 citation needed 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 github repository 3 the source code is released under the terms of version 2 1 of the gnu lesser general public license lgpl 4 it is programmed in c and current source code requires floating point arithmetic although the algorithm itself does not require this the reference software package also includes a frequency division multiplex digital voice software modem and a graphical user interface based on wxwidgets the software is developed on linux and a port for microsoft windows created with cygwin is offered in addition to an apple macos version the codec has been presented in various conferences and has received the 2012 arrl technical innovation award 5 and the linux australia conference s best presentation award 6 technology edit internally parametric audio coding algorithms operate on 10 ms pcm frames using a model of the human voice each of these audio segments is declared voiced vowel or unvoiced consonant codec 2 uses sinusoidal coding to model speech which is closely related to that of multi band excitation codecs sinusoidal coding is based on regularities periodicity in the pattern of overtone frequencies and layers harmonic sinusoids spoken audio is recreated by modelling speech as a sum of harmonically related sine waves with independent amplitudes called line spectral pairs or lsp on top of a determined fundamental frequency of the speaker s voice pitch the quantised pitch and the amplitude energy of the harmonics are encoded and with the lsp s are exchanged across a channel in a digital format the lsp coefficients represent the linear predictive coding lpc model in the frequency domain and lend themselves to a robust and efficient quantisation of the lpc parameters 7 the digital bytes are in a bit field format that have been packed together into bytes these bit fields are also optionally gray coded before being grouped together the gray coding may be useful if sending raw but normally an application will just burst the bit fields out the bit fields make up the various parameters that are stored or exchanged pitch energy voicing booleans lsp s etc for example mode 3200 has 20 ms of audio converted to 64 bits so 64 bits will be output every 20 ms 50 times a second for a minimum data rate of 3200 bit s these 64 bits are sent as 8 bytes to the application which has to unwrap the bit fields or send the bytes over a data channel another example is mode 1300 which is sent 40 ms of audio and outputs 52 bits every 40 ms 25 times a second for a minimum rate of 1300 bit s these 52 bits are sent as 7 bytes to the application or data channel adoption edit codec 2 is currently used in several radios and software defined radio systems freedv 8 flexradio 6000 series 9 sm1000 10 quisk 11 m17 project 12 dtc sentry mesh 6161 manet radio 13 codec 2 has also been integrated into freeswitch and there s a patch available for support in asterisk reticulum s lxst uses codec 2 when operating in ultra low bandwidth profile such as over lora interfaces there was an fm to codec2 digital voice repeater in earth orbit on amateur radio cubesat lilacsat 1 call sign on02cn qb50 constellation which was launched and subsequently deployed from the international space station in 2017 14 history edit the prominent free software advocate and radio amateur bruce perens lobbied for the creation of a free speech codec for operation at less than 5 kbit s since perens did not have the background himself he approached jean marc valin in 2008 who introduced him to lead developer david grant rowe who has worked with valin on speex on several occasions rowe himself was also a radio amateur amateur radio call sign vk5dgr and had experience in creating and using voice codecs and other signal processing algorithms for speech signals he obtained a phd in speech coding in the 1990s and was involved in the development of one of the first satellite telephony systems mobilesat he agreed to the task and announced his decision to work on a format on august 21 2009 he built on the research and findings from his doctoral thesis 15 16 the underlying sinusoidal modelling goes back to developments by robert j mcaulay and thomas f quatieri mit lincoln labs from the mid 1980s in august 2010 david rowe published version 0 1 alpha 17 version 0 2 was released towards the end of 2011 introducing a mode with 1 400 bits s and significant improvements in quantization in january 2012 at linux conf au jean marc valin helped improve the quantization of line spectral pairs which rowe is less familiar with 18 after several changes to the available bit rate modes in winter and spring 2011 2012 2 400 1 400 and 1 200 bit s modes were available after may of that year codec 2 700c a new mode with a bit rate of 700 bit s was finished in early 2017 19 in july 2018 an experimental 450 bit s mode was demonstrated which was developed as part of a master thesis at the university of erlangen nuremberg by clever training of the vector quantization the data rate could be further reduced based on the principle of the 700c mode 20 references edit dcc2011 codec2 vk5dgr pdf archived from the original pdf on 2016 04 14 retrieved 2014 04 25 a pitch energy quantizer for codec2 archived from the original on 2015 06 19 repository for codec 2 source github 14 october 2021 codec2 an open source low bandwidth voice codec slashdot 21 september 2010 arrl board of directors names award recipients at 2012 second meeting www arrl org linux australia 2012 conference retrieved 2012 08 02 cite web cs1 maint deprecated archival service link techniques for harmonic sinusoidal coding pdf archived from the original pdf on 2013 05 15 retrieved 2013 04 12 freedv open source hf digital voice for amateur radio freedv codec2 and the waveformapi archived from the original on 2015 04 02 retrieved 2015 03 06 introducing the sm1000 smart mic rowetel 21 may 2014 quisk a software defined radio sdr james ahlstrom name m17 protocol description github sentry mesh 6161 dtc a codan company dtc a codan company qb 50 constellation satellites deployed from iss american radio relay league website 2017 11 15 retrieved 2019 03 31 techniques for harmonic sinusoidal coding pdf archived from the original pdf on 2013 05 15 retrieved 2013 04 12 open source low rate speech codec part 1 rowetel 21 august 2009 codec2 v0 1 alpha released rowetel 25 august 2010 a pitch energy quantizer for codec2 open source codec encodes voice into only 700 bits per second slashdot 13 january 2017 retrieved 2019 03 31 codec2 hf digital voice at 450 bps southgate amateur radio news 2018 07 08 archived from the original on 2019 03 31 retrieved 2019 03 31 cite web cs1 maint bot original url status unknown link external links edit official website freedv v t e multimedia compression and container formats video compression iso iec mpeg dv mjpeg motion jpeg 2000 mpeg 1 mpeg 2 part 2 mpeg 4 part 2 asp part 10 avc part 33 ivc mpeg h part 2 hevc mpeg i part 3 vvc mpeg 5 part 1 evc part 2 lcevc itu t vceg h 120 h 261 h 262 h 263 h 264 avc h 265 hevc h 266 vvc h 267 enhanced compression model smpte vc 1 vc 2 vc 3 vc 5 vc 6 truemotion and aomedia truemotion s vp3 vp6 vp7 vp8 vp9 av1 av2 chinese standard avs1 p2 avs gb t 20090 2 16 avs2 p2 gb t 33475 2 gy t 299 1 hdr vivid gy t 358 avs3 p2 gy t 368 others apple video avs bink cinepak daala dvi ffv1 huffyuv indeo lagarith microsoft video 1 msu lossless oms video pixlet prores 422 4444 quicktime animation graphics realvideo rtvideo sheervideo smacker sorenson video spark theora thor ut wmv xeb yuls audio compression iso iec mpeg mpeg 1 layer ii multichannel mpeg 1 layer i mpeg 1 layer iii mp3 aac he aac aac ld mpeg surround mpeg 4 als mpeg 4 sls mpeg 4 dst mpeg 4 hvxc mpeg 4 celp mpeg d usac mpeg h 3d audio itu t g 711 a law µ law g 718 g 719 g 722 g 722 1 g 722 2 g 723 g 723 1 g 726 g 728 g 729 g 729 1 ietf opus ilbc speex vorbis flac 3gpp amr amr wb amr wb evrc evrc b evs gsm hr gsm fr gsm efr etsi ac 3 ac 4 dts bluetooth sig sbc lc3 chinese standard avs1 p10 gb t 20090 10 avs2 p3 gb t 33475 3 audio vivid gy t 363 dra gb t 22726 exac sj t 11299 4 others acelp alac asao atrac celt codec 2 isac lyra melp monkey s audio mt9 musepack optimfrog osq qcelp rcelp realaudio sd2 shn silk siren smv svopc tta true audio twinvq vmr wb vselp wavpack wma mqa aptx aptx hd aptx low latency aptx adaptive ldac lhdc llac truehd image compression iec iso ietf w3c itu t jpeg ccitt group 4 gif heic heif hevc jbig jbig2 jpeg jpeg 2000 jpeg ls jpeg xl jpeg xr jpeg xs jpeg xt png apng tiff tiff ep tiff it others av1 avif bpg djvu exr flif icer mng pgf qoi qtvr wbmp webp containers iso iec mpeg es mpeg pes mpeg ps mpeg ts iso iec base media file format mpeg 4 part 14 mp4 motion jpeg 2000 mpeg 21 part 9 mpeg media transport itu t h 222 0 t 802 ietf rtp ogg matroska smpte gxf mxf others 3gp and 3g2 amv asf aiff avi au bpg bink smacker bmp divx media format evo flash video heif iff m2ts matroska webm quicktime file format ratdvd realmedia riff wav mod and tod vob ifo and bup collaborations netvc mpeg la alliance for open media methods entropy arithmetic huffman modified lpc acelp celp lsp wlpc lossless lossy lz deflate lzw pcm a law µ law adpcm dpcm transforms dct fft mdct wavelet daubechies dwt lists comparison of audio coding formats comparison of video codecs list of codecs see compression methods for techniques and compression software for codecs v t e data compression software archivers with compression comparison free and open source 7 zip ark expander file roller freearc info zip kgb archiver paq pax peazip xad decompression only xarchiver zipeg zpaq freeware filzip lha stuffit expander decompression only the unarchiver decompression only tugzip zipgenius commercial arc alzip archive utility arj betterzip macbinary pkzip securezip powerarchiver stuffit winace winrar winzip non archiving compressors generic bzip2 compress gzip lzip lzop pack rzip snappy xz utils zstd for code upx audio compression comparison lossy aac fraunhofer fdk aac nero aac codec faac helix dna producer mp3 l3enc lame toolame libavcodec libcelt libopus libspeex musepack libvorbis windows media encoder lossless alac flac libavcodec monkey s audio mp4als optimfrog shorten wavpack video compression comparison lossy mpeg 4 asp divx nero digital ffmpeg hdx4 xvid h 264 coreavc blu code divx ffmpeg nero digital openh264 quicktime x264 hevc divx x265 others cineform cinepak daala dnxhd helix dna producer indeo libavcodec schrödinger dirac sbc sorenson vp7 libtheora libvpx windows media encoder lossless ffv1 huffyuv lagarith msu lossless yuls see also compression methods and compression formats retrieved from https en wikipedia org w index php title codec_2 oldid 1375555113 categories speech codecs free audio codecs hidden categories articles with short description short description matches wikidata all articles with unsourced statements articles with unsourced statements from september 2020 cs1 maint deprecated archival service cs1 maint bot original url status unknown this page was last edited on 18 september 2026 at 14 30 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal safety contacts code of conduct developers statistics cookie statement mobile view search search toggle the table of contents codec 2 3 languages add topic