SpanDSP is a low-level signal processing library that modulates and demodulates signals commonly used in telephony, such as the "noise" generated by a fax modem or DTMF touchpad.
Thanks, this helped me getting started :)
You need to start with ./bootstrap.sh then ./configure. Maybe also mention the dependencies : make libtool libtiff-dev
README update that references install instructions but also adds it to README