Implement DSP

[MFelida]

DSP Steps

1. Filter audio to match perceived noise. (A weighting as defined in NEN-EN-IEC 61672-1)
2. Calculate RMS
3. Apply time weighting (S weighting as defined in NEN-EN-IEC 61672-1)
4. Convert dBFS to dB SPL

Use CMSIS-DSP features for DSP -- much faster than anything we can write.
3 stages biquad q31 filters look like the best option for now. (Source)