As of this writing, the current version of spandsp is 0.0.6.

Download and extract the spandsp source code as follows:

$ mkdir ~/src/asterisk-complete/thirdparty
$ cd ~/src/asterisk-complete/thirdparty
$ wget http://www.soft-switch.org/downloads/spandsp/spandsp-0.0.6pre17.tgz
$ tar zxvf spandsp-0.0.6pre17.tgz
$ cd spandsp-0.0.6

The spandsp software should compile and install with the following commands:

$ ./configure
$ make
$ sudo make install

This will install the library in the /usr/local/lib/ folder. On many Linux systems this folder is not automatically part of the library path (libpath), so it will need to be added manually.

In order to make the spandsp library visible to all applications on the system, the folder where it is located must be added to the libpath for the system. This is typically done by editing files in the /etc/ld.so.conf.d/ directory. You simply need to ensure that one of the files in that directory has /usr/local/lib listed. If not, the following command will create a suitable file for you:

$ sudo cat >> /etc/ld.so.conf.d/usrlocallib.conf
/usr/local/lib

Press Ctrl+D to save the file, then run the ldconfig command to refresh the library paths:

$ sudo ldconfig

You are now ready to recompile Asterisk for spandsp support.

Since the spandsp library was probably not installed on the system when Asterisk was first compiled, you will need to do a quick recompile of Asterisk in order to have the spandsp support added:

$ cd ~/src/asterisk-complete/asterisk/1.8/
$ ./configure
$ make menuselect

Ensure that under the Resource Modules heading, the section for spandsp looks like this:

[*] res_fax_spandsp

If you see this instead:

XXX res_fax_spandsp

It means that Asterisk was not able to find the spandsp library.

Once you have verified that Asterisk can see spandsp, you are ready to recompile. Save and exit from menuselect, and run the following:

$ make
$ make install

You can verify that spandsp is working with Asterisk by issuing the following command from the Asterisk CLI:

*CLI> module show like res_fax_spandsp.so

At this point the SendFAX() and ReceiveFAX() dialplan applications will be available to you.

The spandsp library and the Digium fax library, discussed in the next section, are mutually exclusive. If you want to try out the Digium fax product, you will need to ensure that spandsp does not load. To disable spandsp in Asterisk, simply edit your /etc/asterisk/modules.conf file as follows:

noload => res_fax_spandsp.so

Save the changes and restart Asterisk.