I'm playing with Teensy again after some time away. I'm just getting into the amazing audio library- it's very impressive. I'm using the built-in ADC for the input signal. The AudioAnalyzeFFT1024 is almost, but not quite what I want:
"Compute a 1024 point Fast Fourier Transform (FFT) frequency analysis, with real value (magnitude) output. The frequency resolution is 43 Hz, useful detailed for audio visualization."
The signal I'm interested in (from the ultra-cheap HB100 doppler microwave sensor) has useful output signals down below 10 Hz for slowly moving objects. This particular device runs at 10.525 GHz and the output frequency for a given velocity is (f/31.37) mph. For example a walking speed at 3 mph gives you a 94 Hz output. If your FFT resolution is 43 Hz, that means your speed bins are 1.4 mph wide and it is hard to resolve slower-moving objects as they all fall into the [0] bin (DC term). So I'd like to run the ADC at least 4x more slowly, say 11 kHz instead of 44.1 kHz if that's what it is at now. Is that possible, and if so how? If the ADC sample rate is too linked into the design to change, can I somehow decimate the input 4x before the FFT? (I'm fine with a kludgy hack inside the library, if that's possible.) Thanks for any hints!
"Compute a 1024 point Fast Fourier Transform (FFT) frequency analysis, with real value (magnitude) output. The frequency resolution is 43 Hz, useful detailed for audio visualization."
The signal I'm interested in (from the ultra-cheap HB100 doppler microwave sensor) has useful output signals down below 10 Hz for slowly moving objects. This particular device runs at 10.525 GHz and the output frequency for a given velocity is (f/31.37) mph. For example a walking speed at 3 mph gives you a 94 Hz output. If your FFT resolution is 43 Hz, that means your speed bins are 1.4 mph wide and it is hard to resolve slower-moving objects as they all fall into the [0] bin (DC term). So I'd like to run the ADC at least 4x more slowly, say 11 kHz instead of 44.1 kHz if that's what it is at now. Is that possible, and if so how? If the ADC sample rate is too linked into the design to change, can I somehow decimate the input 4x before the FFT? (I'm fine with a kludgy hack inside the library, if that's possible.) Thanks for any hints!