I thought I was nearly there but can't quite get it over the line. about arduinofft

[DrJaymz]

micDataImag = 0; <--- duh.
micDataImag[i] = 0;

[DrJaymz]

The sampling frequency is 64000hz. I am using the m5stack core 2 built in spm1423 microphone. I tried 22000, then 44100 and 48000 and at 64000 I got the best sound. My window size is 512 samples.
The microphone is a PDM microphone not PCM, but I'm told that the I2S driver interface takes care of that weird format and all I need to do is just read. I couldn't find any useable documentation on any of that - but I found a demo someone else had done also using 64000 and used the same settings. Whether or not PDM leads to different effective sample rates than PCM I have no idea. But the fundamental frequency emitted from ardiuinoFFT when I use a 1kHz tone is 1.000Khz. So - guess it must be correct.

[blaz-r]

Hello,
so with this fix, the code is working as it should now?

Also, if you are doing this in a loop, it might be worth initializing memory outside of it, so you don't allocate and free every iteration, as that is just wasting time. Also, you can use new in c++ and then delete[] to deallocate it, which is a bit nicer than malloc. Or you can init array on stack/data segment without malloc or new if you know the size beforehand, like: double data[size];

[DrJaymz]

Well not really with that code. I found that it worked if I specified on the constructor as below but not as I showed it there;

double vReal[512];
double vImag[512];
arduinoFFT FFT = arduinoFFT(vReal, vImag, 512, 64000);

Then call:

  FFT.Compute(FFT_FORWARD);
  FFT.ComplexToMagnitude();
  double peak = FFT.MajorPeakParabola(); 

Then I get something sensible. I wasn't sure what FFT functions I needed to call before FFT.MajorPeakParabola();
But this seemed to work. No idea if I needed to remove DC or not beforehand, but I don't think it changes anything.

There were other problems with the I2S sampling. I just wanted to get to the point where the mic was being sampled via I2s continually and I could just drop in when I felt like it and grab 512 samples and get the most dominant frequency.
I have it working but its a bit messy to integrate with my existing code right now.

What I really need is a bandpass filter, which I think I will can do on the samples directly before passing into fft.

[kosme]

@DrJaymz, I see a problem with the setup you describe. The sampling rate should be at least twice the highest expected frequency. Since you mention that you can hear yourself speaking, I infer you are dealing with audio. Therefore, the sampling frequency should be at least 44000.