There are 4 repositories under dsp-library topic.
C++ Library for Audio Digital Signal Processing
DSP library for signal processing
Digital Signal Processing(DSP) Guide
A basic (soft) dsp library for arduino and most of the microcontrollers which can be programmed in C/C++
IIR filters coefficient generation for ARM CMSIS DSP library using GNU Octave Script.
Some useful DSP and Math functions focusing on embedded systems