A nice set of links to AudioCoding information. Since this is a Wiki site, it is highly collaborative - registered users can provide updates and modifications to the site at will. (I think.)

http://www.audiocoding.com/wiki/

Nellymoser is the leading provider of proprietary speech and audio software technology and solutions in the areas of compression, modification, synchronization and conversion. Our products improve speech and audio quality and efficiency in bandwidth-constrained environments while creating more immersive, interactive environments for your applications and services.

http://www.nellymoser.com/

The Asao libraries from Nellysoft have been designed specifically to address the need for a very small footprint, low bandwidth speech and audio compression. Asao will operate at a variety of bit rates (12/16/24/32 Kbps). This new technology can be rapidly harnessed for applications such as streaming over mobile data networks, Internet radio and embedded platforms such as toys and other consumer devices.

http://www.nellymoser.com/products/audio_compression_asao_fst.htm

The Sase libraries fron Nellysoft offer flexible compression options for both embedded and data packets based compression implementations It can operate in either a single bit rate or a multi-rate mode, offering compression rates (1.8/3.2/6.4 Kbps) to suit your application or the changing environment of packet based networks. Sase has the ability to switch bit rates on-the-fly to better handle changing network condition. At 3.2 Kbps Sase offers near toll quality, as you would expect when more bits are added the speech quality improves at 6.4 Kbps.

http://www.nellymoser.com/products/compression_fst.htm

The voice recording applet SDK is designed for the web developers and allows to record the voice from web site, to compress it and to send to the web server via HTTP. To playback the recorded voice from the server the embedded voice streaming player or a separate player as a voice streaming applet can be used. Both applets are designed in Java 1.1 and has a JavaScript interface.

http://www.vimas.com/ve_record_applet_sdk.htm

Intel has created a new library designed to deal with varous primitives used in Data Compression. Intel says: Intel® Integrated Performance Primitives (IPP) is a software library which provides a range of library functions for multimedia, audio codecs, video codecs (for example H.263, MPEG-4), image processing (JPEG), signal processing, speech compression (i.e. G.723, GSM ARM*) plus computer vision as well as math support routines for such processing capabilities.Unlike their previous libraries, this is now a commercial product which is going to cost you as much as $199. Works with Windows and Linux.

http://developer.intel.com/software/products/ipp/ipp30/overview.htm

Source code for A 2.4 Kbps MELP coder. Target is Sun OS4. Phil Frisbie did the detective work needed to determine that the MELP coder is now owned by ASPI, so if you want to use it, you need to talk to them about licensing. See them at www.aspi.com.

http://www.data-compression.com/melp1.2.tar.gz

UCSB research activities, including speech coding, audio compression, video coding. Lots of links to demos and publications.

http://scl.ece.ucsb.edu/index.htm

Source code and documentation of some nice low bit rate speech coding.

http://maya.arcon.com/ddvpc/melp.htm

The Wikipedia talks about LPC. A very short definition.

http://en.wikipedia.org/wiki/Linear_predictive_coding

The Wikipedia article on speech coding. A very few good definitions, and a very few good links.

http://en.wikipedia.org/wiki/Speech_coding

A company named Effnet Inc. is licensing a version of CRTP, a protocol that compresses packet headers in RTP streams. With small VOIP packets this can provide substantial savings.

http://www.eet.com/story/OEG20020108S0054

Part of a Master’s Thesis on voice compression, in Italian.

http://www.cs.brandeis.edu/~gim/Papers/Cefriel.pdf

VoiceAge, of Montreal, announces the “Open G.729(A) Initiative,” which allows developers to freely use their G.729(A) codec object code for non-commercial purposes. This initiative provides you with an opportunity to work with the G.729(A) codec for free while developing products or applications. Take advantage of voice compression to prove that VoIP works efficiently and provides good voice quality.

Note: this site went all-Flash - which means you will have to navigate to the Open G.729 page manually.

http://www.voiceage.com/

Atlanta Signal Processor, Inc., is nice enough to host his paper on their site. It gives a brief overview of the MELP Vocoder algorithm.

http://www.aspi.com/tech/specs/pdfs/melp.pdf

Apple has published a tech note describing the differences between these two file formats, which on the face of it ought to be identical.

http://developer.apple.com/technotes/tn/tn1081.html

Spirit has a wide variety of speech codecs for sale, including standard G.711, G.729 and so on, all the way down to proprietary 1200 bps coders.

http://www.spiritcorp.com/vocoders.html

This RFC defines the 32 Kbps toll quality MIME type. The true specification for G.726 is owned by the ITU, and will not be generally available on the net. So knowing how it is encoded only somewhat useful.

http://www.faqs.org/rfcs/rfc2422.html

An ftp site with various speech codecs, including G.722, GSM, G.711, G.723, G.721, CELP, and LPC. Licensing and ownership of the C source varies.

ftp://ftp.cs.cmu.edu/project/fgdata/speech-compression/

Zarak Systems will perform Quality of Service testing using PSQM, the Perceptual Speech Quality Measurement. This web page will tell you a little bit about what that means to you.

http://www.psqm.com/