SpeechCompression of human speech is a specialized form of audio compression. Greater levels of compression can be achieved by modeling the human vocal tract, and taking advantage of redundancy in human speech.
Books
Digital Processing of Speech Signals
by Lawrence R. Rabiner, Ronald W. Schafer. A basic overview of how to use DSP to deal with speech.
Computer Speech : Recognition, Compression, Synthesis
by Manfred R. Schroeder. How about a customer review of this book?
Commercial Libraries
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.
The folks at Compandent have this to say about their product: Compandent's ComPacketer is a voice coder which achieves a breakthrough in quality/bit rate/complexity tradeoff. Compandent’s novel technology, the ComPacketer that operates at 2.8 kb/s, produces speech with quality which exceeds that of ITU-T G.723.1 at 6.3 kb/s. Using the ComPacketer, only graceful degradation is introduced in frame erasure environment, as compared to the higher quality degradation introduces by the common standards used for VoIP.
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.
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.
It's a little hard for me to tell what Epigon is selling. They have a nice picture of some kind of board on their front page, but I don't think they have any hardware for sale. They do appear to have audio codecs for MPEG-1, MPEG-2, and MPEG-4, as well as what appears to be a proprietary speech codec called eSpeech.
Note: Reader Ragu says that despite the problem siwith the web page, he is a big fan of their products. He is a satisfied customer who feels their audio codecs are the best.
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.
These folks make several different G.729 and G.723.1 codecs,
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.
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.
GAO Research Speech Codec Software
GAO Research sells speech codecs for quite a few different platforms, including a big batch of DSP parts. They support a wide varity of ITU formats, including G.729, G.711, G.722, and more.
Hawk Software Commercial Speech Codecs
Hawk Software is now selling a pair of codecs, LPC-10 and OpenLPC, that are suitable for Windows CE, CELinux, and other 32-bit embedded platforms. More are planned for future releases.
The EasyAudio ActiveX Control adds speech handling capabilities to your Win32 program. Listed features include nice things such as support for popular codecs including G.729, G.711, and ADPCM, unicast and multicast support, AGC, jitter buffer management, and noise reduction. The web page gives a price of $1000 for the control, and $2000 for the source code. I hope that big price tag includes free distribution rights, but the web site is woefully short on license information. Version 3.0 is shipping as of March, 2003.
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.
Intel Integrated Performance Primitives
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.
Commercial Programs
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.
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.
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.
This product takes your text, converts it to speech, then stores the result in one of several compressed formats, including MP3, Ogg Vorbis, and G.721.
Companies/Organizations
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.
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.
This is the home page for the IETF group that reviews RTP packetization standards. Links on this page for all the drafts you can imagine for sending video and audio over RTP streams.
These folks make several different G.729 and G.723.1 codecs,
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.
Algorithm cuts VoIP bandwidth requirement
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.
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.
IstraSoft appears to make some speech codecs, supplied as Windows DLLs. Plus some discussion on their web page re: English phonetics.
Courses/Seminars
What appears to be a course or lecture outline on speech coding.
Files
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.
Hardware
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.
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.
Italian
Compressione della voce a 2.4 Kbit/s
Part of a Master's Thesis on voice compression, in Italian.
Links
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.)
This site contains the comp.speech FAQ, and also has links to their ftp site, which contains software for speech codecs.
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.
A page on speech compression by Nam Phamd. Concentrates on LPC and CELP.
GSM 06.10 lossy speech compression
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.
Newsgroup Posts
What is mu-law encoding? Where can I get source for it?
Part of the DSP FAQ, in our case it is an answer to a speech coding question.
Non-Commercial Libraries
This open source project aims to create a free H.323 stack. The project was started as a reaction to the high cost of commercial implementations of audio and video compression code implementing the various components of H.323. Roger H. adds There are now several useful applications which use the library including OpenMCU (a reliable multi person conference server) and GnomeMeeting (a GTK/Gnome GUI client for Linux/BSD Unix.
Version 1.13.13 of OpenH323 shipped in Marh, 2004.
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.
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.
A low bitrate codec, described as being derived from the work of Ron Frederick. Freeware.
The Speex project aims to build a patent-free, Open Source/Free Software voice codec. Unlike other codecs like MP3 and Ogg Vorbis, Speex is designed to compress voice at low bitrates in the 8-32 kbps/channel range. Possible applications include VoIP, internet audio streaming, archiving of speech data (e.g. voice mail), and audio books. In some sense, it is meant to be complementary to the Ogg Vorbis codec.
Speex 1.1.5 was released in April, 2004.
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.
Non-Commercial Programs
This project is an attempt to port the free Speex voice codec to a pure Java implementation.
Version 0.9.4 is shipping as of June, 2004.
OTR stands for "Old Time Radio". The owners of this project want to be able to listen to classic mono AM radio recordings on their Sharp PDAs.
Papers/Documentation
This site contains the comp.speech FAQ, and also has links to their ftp site, which contains software for speech codecs.
Atlanta Signal Processor, Inc., is nice enough to host his paper on their site. It gives a brief overview of the MELP Vocoder algorithm.
Very Low bit rate speech coding
A project at Cambridge University that led to a low bit rate speech coder that was used in the HP 620LX Palmtop PC.
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.
Compressione della voce a 2.4 Kbit/s
Part of a Master's Thesis on voice compression, in Italian.
UCSB research activities, including speech coding, audio compression, video coding. Lots of links to demos and publications.
SHORTEN: Simple lossless and near-lossless waveform compression
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.
All the voice coding specs you can shake a stick at. Get your checkbook out, though, these aren't free.
Interpolative Coding at 2.8 kbps
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.
Differences Between Microsoft and Apple ADPCM Files
Apple has published a tech note describing the differences between these two file formats, which on the face of it ought to be identical.
Results
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.
Source Code
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.
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.
A low bitrate codec, described as being derived from the work of Ron Frederick. Freeware.
This is reputed to be C source code for a GSM codec.
GSM 06.10 lossy speech compression
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.
The Speex project aims to build a patent-free, Open Source/Free Software voice codec. Unlike other codecs like MP3 and Ogg Vorbis, Speex is designed to compress voice at low bitrates in the 8-32 kbps/channel range. Possible applications include VoIP, internet audio streaming, archiving of speech data (e.g. voice mail), and audio books. In some sense, it is meant to be complementary to the Ogg Vorbis codec.
Speex 1.1.5 was released in April, 2004.
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.
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.
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.
Source code and documentation of some nice low bit rate speech coding.
This project is an attempt to port the free Speex voice codec to a pure Java implementation.
Version 0.9.4 is shipping as of June, 2004.
This is supposed to be a 2.4 Kbps LPC speech codec.
Standards
RFC 2422 - G.726 - 32 Kbps ADPCM codec
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.
Tutorials, Reference, Presentations
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.)
This site contains the comp.speech FAQ, and also has links to their ftp site, which contains software for speech codecs.
A page on speech compression by Nam Phamd. Concentrates on LPC and CELP.
GSM 06.10 lossy speech compression
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.
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.
Digital Speech Compression - Putting the GSM 06.10 RPE-LTP algorithm to work
An article by Jutta Degener describing implementation of this GSM codec.
Wikipedia entry: Linear Predictive Coding
The Wikipedia talks about LPC. A very short definition.
Wikipedia entry: Speech Coding
The Wikipedia article on speech coding. A very few good definitions, and a very few good links.
UCSB research activities, including speech coding, audio compression, video coding. Lots of links to demos and publications.
