`lib_dsp` has functions for doing adaptive filtering: [LMS](https://github.com/xmos/lib_dsp/blob/develop/lib_dsp/api/dsp_dct.h) and [NLMS ](https://github.com/xmos/lib_dsp/blob/develop/lib_dsp/src/dsp_adaptive.c#L48). Should probably add these here.
