If you have BL_Heli32 or BlueJ ESCs and have bidirectional DShot enabled, it’s worth adjusting the RPM filters as well. To do this, switch in Blackbox Explorer from the frequency view to the Frequency vs. Throttle view via the dropdown menu at the top left. In the image below, you’ll notice two red curves.

• The first curve starts around 150 Hz and rises toward the top right corner.
• The second curve starts around 160 Hz and is flatter than the first.

Both curves reflect vibrations caused by the motors and propellers. The first curve shows the actual vibrations, while the second curve is the harmonic of the first fundamental vibration.

Even if only two curves are visible in the image, never select fewer than 3 harmonics for the RPM filters. Set the minimum frequency to the frequency where the first curve begins. In the example above, I used 3 harmonics and a minimum frequency of 145 Hz. With these settings, these vibrations were completely filtered out.

To minimize the filter latency of the RPM filters, the Q-factor can be increased, which narrows the filter band. Betaflight doesn’t provide a direct input field for this in the GUI, but you can adjust it via CLI using the command:

set dyn_notch_q = <value>

The default value is 500, but with a well-filtered signal, it’s often beneficial to increase it to 750 or 1000. In the following example, I set a Q-factor of 1000—the filtering remains sufficient, while the filter latency is minimized.