A low bitrate codec, described as being derived from the work of Ron Frederick. Freeware.

ftp://ftp.futuredynamics.com/OpenLPC/

Some speech samples that have been encoded at various rates using various codecs. If you’ve never heard speech encoded at 1.4 Kbps, here’s a chance to check it out.

http://www.hawksoft.com/hawkvoice/codecs.shtml

HawkVoice is a game oriented, multiplayer voice over network API released under the GNU Library General Public License (LGPL), with
support for Linux/Unix and Windows 9x/ME/NT/2000. It is designed to be a portable, open source code alternative to DirectPlay(R) Voice in DX8.

http://www.hawksoft.com/hawkvoice/

An article by Jutta Degener describing implementation of this GSM codec.

http://www.ddj.com/articles/1994/9412/9412b/9412b.htm

Part of the DSP FAQ, in our case it is an answer to a speech coding question.

http://www.hr/josip/DSP/FAQ/27.html

The DSP Group makes a codec called TrueSpeech. You can get a copy of the player for free here to check out the 8.5 KBps audio it makes possible.

http://www.dspg.com/dspg/truespeech_compression.html

This freeware program is designed to perform Internet telephony. It incorporates source for a couple of interesting speech codec, which is why it gets a link in the library.

http://www.speakfreely.org/

IstraSoft appears to make some speech codecs, supplied as Windows DLLs. Plus some discussion on their web page re: English phonetics.

http://www.istrasoft.com/

Descriptions of various speech codecs, include G.711, G.721, GSM, and CELP. Each codec gets a brief description plus pointers to additional material and source code.

http://rice.ecs.soton.ac.uk/jason/speech_codecs/standards/index.html

A page on speech compression by Nam Phamd. Concentrates on LPC and CELP.

http://www.data-compression.com/speech.html

This is supposed to be a 2.4 Kbps LPC speech codec.

http://www.arl.wustl.edu/~jaf/lpc/

This is reputed to be C source code for a GSM codec.

ftp://ftp.cs.tu-berlin.de/pub/local/kbs/tubmik/gsm/gsm-1.0.10.tar.gz

by Lawrence R. Rabiner, Ronald W. Schafer. A basic overview of how to use DSP to deal with speech.

http://www.amazon.com/exec/obidos/ASIN/0132136031/theinternetdatac

by Manfred R. Schroeder. How about a customer review of this book?

http://www.amazon.com/exec/obidos/ASIN/3540643974/theinternetdatac

A project at Cambridge University that led to a low bit rate speech coder that was used in the HP 620LX Palmtop PC.

http://svr-www.eng.cam.ac.uk/~ajr/speechCoding.html

This site advertises a bunch of nifty looking codecs, including TELP, JPEG, Speech, MPEG, and wavelet compressors. I can’t quite determine exactly what form the products come in.

http://www.gt-tech.com/technology.html

Nuera makes a couple of speech multiplexers that use CELP compression. You probably won’t be interested in these unless you’ve got a T1 line that is bursting at the seams.

http://www.nuera.com/products/AP200_100.cfm

All the voice coding specs you can shake a stick at. Get your checkbook out, though, these aren’t free.

http://www.itu.int/itudoc/itu-t/rec/g/g700-799/index.html

These folks make several different G.729 and G.723.1 codecs,

http://www.sipro.com/

Our technology served as the foundation for numerous voice compression products used by voice portal and large multinationals in their efforts to better meet the quality requirements that end users. As example voice email, voice chatting, voice annotation in web site. Our technology is already integrated into software by companies such as Microsoft with its Netshow® software and in its Mediaplayer®, and RealNetworks within its RealAudio® and RealVideo®. In addition, over the last decade this compression technology (over 100 patents) was positioned in several International Telecommunication standards, notably: GSM ,PCS, TDMA ,CDMA, TETRA, G.729 . VoiceAge’s compression technology is well positioned at cross road of internet and voice for next-generation of voice portal.

http://www.voiceage.com

These folks at UCSB are encoding speech at 2.8 Kbps. It sounds very good considering the bit rate. Links here to a presentation and an abstract, as well as some samples.

http://scl.ece.ucsb.edu/current/oded/ewi_demo.htm

These folks offer some seminars on communcations. On their page, if you go to the links to free software, you will find Matlab code for CELP and LPC Vocoders. This same page also has a wide variety of links for speech coding stuff.

http://www.cysip.com/

A web site containing the comp.speech FAQ. In particular, you will be interested in section 3 for this FAQ, which discusses speech coding and compression.

http://svr-www.eng.cam.ac.uk/comp.speech/

GSM provides telephone quality speech at a compressed rate of 13 Kbps. Compare this to the 64 KBps required by standard u-law and A-law codes. This site gives lots of info about the GSM format, along with free source code.

http://kbs.cs.tu-berlin.de/~jutta/toast.html

This company makes the AMBE-2000, a Vocoder chip that compresses speech down to a miniscule 4 Kbps. They have an additional product library of low bit-rate codes both in hardware and software.

http://www.dvsinc.com/

This site contains the comp.speech FAQ, and also has links to their ftp site, which contains software for speech codecs.

http://www.speech.cs.cmu.edu/comp.speech/

Tony Robinson - Technical report CUED/F-INFENG/TR.156. A report on an audio compression algorithm that relies on compression of the waveform with Huffman compression of the residuals.

http://svr-www.eng.cam.ac.uk/~ajr/tr156/tr156.html

Typical clinical MRI scanners generate data on the order of about 200 MB each day. Because this data provides important diagnostic information, care must be taken in compressing it, and lossy compression is generally avoided. In this project we investigate different techniques for lossless compression of 3-dimensional MRI scans of the brain. These methods include predictive coding, “model coding” using a reference data set, background suppression, symmetry coding and pyramid coding

Matlab source code is included along with the full text of the paper.

http://www-ise.stanford.edu/class/ee392c/demos/hargreaves_johanson_nayak/

What appears to be a course or lecture outline on speech coding.

http://svr-www.eng.cam.ac.uk/~ajr/SA95/node78.html