libcm is a C application development framework with an emphasis on audio signal processing.

Some of its features are:

• entirely written in C
• very few external dependencies (ALSA,FFTW,Atlas)
• a real-time audio/MIDI system
• a dataflow system
• many audio processing algorithms implemented in plain C.
• file readers and writers for WAV,AIFF,MIDI,CSV,MusicXML,XML among others

libcm is big. The best way to get a sense of what is in it is to browse the documentation files here.