Speex: A Free Codec For Free Speech
Overview
Speex is an Open Source/Free Software patent-free audio compression format designed for speech. The Speex Project aims to lower the barrier of entry for voice applications by providing a free alternative to expensive proprietary speech codecs. Moreover, Speex is well-adapted to Internet applications and provides useful features that are not present in most other codecs. Finally, Speex is part of the GNU Project and is available under the revised BSD license.
The Technology
Speex is based on CELP and is designed to compress voice at bitrates ranging from 2 to 44 kbps. Some of Speex's features include:
- Narrowband (8 kHz), wideband (16 kHz), and ultra-wideband (32 kHz) compression in the same bitstream
- Intensity stereo encoding
- Packet loss concealment
- Variable bitrate operation (VBR)
- Voice Activity Detection (VAD)
- Discontinuous Transmission (DTX)
- Fixed-point port
- Acoustic echo canceller
- Noise suppression
Note that Speex has a number of features that are not present in other codecs, such as intensity stereo encoding, integration of multiple sampling rates in the same bitstream (embedded coding), and a VBR mode; see our comparison page for more.
Getting Involved
One of the simplest things you can do to get involved in Speex is by using it in your application; Speex is well-suited to handle VoIP, internet audio streaming, data archival (like voice mail), and audio books. Currently, LinPhone, Ekiga, and Asterisk are some of the projects currently using Speex. For a list of projects with Speex support, visit our Plugins & Software page.
If you have questions or are interested in contributing to the project, have a look at our roadmap, join our mailing list, or send us money so we can keep working on Speex. You can also contact the Project Lead, Jean-Marc Valin (though the mailing is usually the best place to ask questions).
Headlines
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Speex 1.2beta3 is out
December 11, 2007
The most obvious change in this release is that all the non-codec components (preprocessor, echo cancellation, jitter buffer) have been moved to a new libspeexdsp library. Other changes include a new jitter buffer algorithm and resampler improvements/fixes. This is also the first release where libspeex can be built without any floating point support. To do this, the float compatibility API must be disabled (--disable-float-api or DISABLE_FLOAT_API) and the VBR feature must be disabled (--disable-vbr or DISABLE_VBR).
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Speex 1.2beta2: Fixed-point improvements and more
May 24, 2007
Again, this new releases brings many improvements. The RAM requirement for wideband has gone down drastically (i.e. more than 2x). A new resampler module has been added, providing arbitrary sampling rate conversion -- fast. The echo canceller has also been improved. A bug in 1.2beta1 that made the echo canceller unstable has been fixed. The echo canceller should now converge faster, be robust and tolerant of incorrect capture-playback synchronisation. The preprocessor has also been greatly improved. Not only should the quality be better, but it is now fully converted to fixed-point. At last, early TriMedia support (incomplete) has been merged.
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Speex 1.2beta1: Better, smaller, faster and more
September 4, 2006
This new release brings many significant improvements. The quality has been improved, both at the encoder level and the decoder level. These include enhancer improvements (now on by default), input/output high-pass filters, as well as fixing minor regressions in previous 1.1.x releases. A strange and rare instability problem with pure sinusoids has also been fixed. On top of that, memory use has been greatly reduced, especially for fixed-point and narrowband. The fixed-point narrowband encoder+decoder memory use has been cut by more than half, making it possible to fit both in less than 6 kB of RAM. In general, CPU requirement had gone down, especially for the fixed-point port. The Blackfin port has been speeded up significantly, thanks to David Rowe. There are also a few fixes for the TI C5X DSPs, as well as better support for C++ compilers and crappy MS compilers. Oh, and before anyone starts worrying, the format (bit-stream) itself has not changed, so Speex is still compatible with version 1.0 and will continue to be in the future.
Non-codec improvements include a extension (easier to use) to the echo canceller API and a Speex-independent version of the jitter buffer. The echo canceller should also be more robust to saturation in the capture path. Last, but not least, the documentation has been updated.
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How the Echo Canceller works
August 7, 2006
Always wanted to know how the Speex echo canceller works? On Adjusting the Learning Rate in Frequency Domain Echo Cancellation With Double-Talk has just been accepted for IEEE Trans. on Audio, Speech and Language Processing.