Tasks Accomplished:

• Worked closely with Ram to setup single microphone sampling using the DFSDM. Currently, we’ve verified that the 8 kHz output sampling rate can be continuously written to and read from memory via the DMA
• DFSDM unfortunately does not have built-in capability to do band-pass filtering. Based on this link (pg 11/56), a digital microphone typically has a 4th order sigma-delta modulator with strong off-band quantization noise. We anticipate we will require possibly a 5th order Sinc filter but would require looking at gathered data/fourier-transforms to get better insight.
• CMSIS conveniently provides a sample (here is just some link to some sample code) for implementing FIR filters. FIR filters depending on the coefficients and windowing can be used to generate a software filter. The annoying part is determining the FIR coefficients. ScopeFIR (commercial software with a trial) allows for specifying frequency bounds and various window settings and # coefficients for filter design. The image below is an example. Fine-tuning the filter (if needed) will be next week’s task.
  

Deliverables this week:

• Close work with Ram to get a 2 mic sampling setup working
• Integrate 2 mic sampling with osxAcousticSL (anticipate some fiddling with DMA settings and such)
• Based on FFT analysis, figure out the exact filter parameters and targets we need (in reverse, we may not need a filter!)