Real time audio spectrum plot (from the MIC)

App gets audio data from microphone and plots the real time spectrum in the form of a scrolling image.

App settings:
- Sample Rate = the Sample Rate (in Hz) at which the microphone will be read. The app does not restrict the entered value, however for unsupported Sample Rates, the plot will simply not start. Most devices usually support 8000, 44100, 48000 Hz, etc.
- FFT Buffer Size = the size (in samples) of the audio buffer used to compute the FFT. Must be a power of 2, min = 128, max = 16384. Bigger value gives better frequency resolution. Smaller value gives better time resolution.
- Min. Displayed Frequency
- Max. Displayed Frequency
- Gain
- Displayed Time Window (in milliseconds)
- Frequency Grid Step (in Hz) = will draw horizontal division lines
- Time Grid Step (in milliseconds) = will draw vertical division lines moving together with the plot.
- Theme = app UI theme (light / dark). Affects only the UI. Does not affect the plot colors.