How to read the FFT noise spectrum
The FFT is the map of your noise. Read the peaks and you know instantly whether motors, props, frame or the D-term are the source — and whether the filters are hitting it.
What the FFT shows
The FFT breaks the gyro signal into its frequency components: the x-axis is frequency (Hz), the height is how strong the noise is there. Noise isn't just noise — the frequency reveals the cause.
Reading peaks: motor, prop, frame
Sharp peaks that move with throttle are motor harmonics. A fixed peak that doesn't move is usually a frame resonance. A single conspicuous peak can be a damaged or unbalanced prop.
Filtered vs. unfiltered
The real test is overlaying filtered against unfiltered gyro: the difference shows exactly what your filters removed — and what still gets through. For that you need the debug mode with the unfiltered gyro.
PIDoctor labels the spectrum
Instead of reading peaks by hand, PIDoctor overlays motor harmonics and filter cutoffs on your FFT and labels what is motor noise, D-term noise or resonance — and whether your filters cut where the noise sits.