I was able to get big improvement on a siren detector by increasing the FFT size to 512 and the Filters to 64. Unfortunately, the DSP now takes 6sec for 2sec of audio. The Adafruit NRF52 board defs do not seem to support CMSIS for the DSP. It only takes about a 1sec of DSP on the Arduino Nano, which is built on MBed and supports CMSIS. I tried to force CMSIS for the DSP using EIDSP_USE_CMSIS_DSP & EIDSP_LOAD_CMSIS_DSP_SOURCES but I get the following error:

```
/src/edge-impulse-sdk/dsp/spectral/../numpy.hpp:1133: undefined reference to `arm_rfft_fast_f32'
/src/edge-impulse-sdk/dsp/spectral/../numpy.hpp:1141: undefined reference to `arm_rms_f32'
```

I am in way over my head, but it looks like support for CMSIS v5 has been included:

Is there a way to enable CMSIS-DSP support for CMSIS capable boards not based on MBed?