SpanDSP is a library of Digital Signal Processing (DSP) functions for telephony. One of its common uses is to provide 'that thing' that is needed to turn images into audio and back (and a lot of other things) for sending and receiving faxes. Support exists for using SpanDSP with iaxmodem, Asterisk, CallWeaver, and FreeSwitch.

SpanDSP is developed by Steve Underwood. Its web site is and the latest version can be downloaded from

At the time of this writing, the latest version of spandsp is 0.0.6pre17. Some distributions/OSs may provide pre-packaged versions:
  • Gentoo provides 0.0.6_pre12
  • Debian provides 0.0.5~pre4 for lenny and sid
  • Ubuntu 9.10 provides 0.0.5pre4 while 8.04-3 provides 0.0.4pre16
  • add your favourite distro here.

If you build spandsp from sources, it requires at least (be sure to have the dev or devel versions of those libraries installed if your distribution/OS provides them as separate packages):
The official installation instructions are located at

SpanDSP as a FAX machine for Asterisk 1.6.X

G.711 and T.38 FAX support is built into Asterisk, through the use of the Spandsp library. The Spandsp library itself must be manually added. See the Asterisk T.38 page for detailed installation instructions.

SpanDSP as a FAX machine for Asterisk 1.4.X

SpanDSP supports FAXing at speeds up to 14,400bps V.17, and works with or without ECM (error correction mode).

Although I have not yet tested this myself (I will later and hopefully update here later) here are some links that should be able to enable you to apply SpanDSP to Asterisk 1.4.X.

Third Party Application

The following third party applications provide support for Spandsp and add additional functionality
AGX Extra Addons for Asterisk provide some fax applications that uses spandsp and works with Asterisk 1.4.

See also

Created by: pupeno, Last modification: Tue 30 of Mar, 2010 (10:02 UTC) by spamblock
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