What 8 parameters are set by the Harmonic Notch Filter section of the Extended Tuning page?

I asked about this section of the Extended Tuning Page in a previous post. The responses were helpful - but still didn’t provide the key information I’m looking for.

There are 8 setting on this page:

This group of 8 settings are labeled as Harmonic Notch Filter.

I had assumed that these were all involved in the FFT Harmonic Notch Filter - but now I’m wondering if it’s something beyond that.

As the latest FFT sets all of the notch filter parameters automatically, does this screen simply report on some of those values?

Is there ever a reason to use this screen to change some of these values?

look at the INS_HNTCH.* params

Yea. Set them on that screen or the Full Parameter List, your choice. It doesn’t report on any FFT parameters other than to indicate if FFT is used as reference (Mode).


The values are probably there just because it’s a part of the extended tuning of a vehicle. You can change them there but I always use the full parameter list. I guess it’s just to make it easier to do changes.

I understand your confusion around the FFT. So, the harmonic notch is a filter used to reduce noise that the computer sees. The noise is still there since it’s mostly generated mechanically from the airframe and so on. The filter only removes it in the eyes of the computer so that the noise is filtered out from the values the computer uses for stabilization.

For the filter to work, you need a way to detect the noise. The FFT is one way of detecting noise. So the filter and FFT settings are two different things even if the FFT sets the filter settings automatically. Those settings will probably need some tuning anyways.

There is also other ways of detecting noise. So the filter can be used without the FFT. You can use motor rpm (needs telemetry from ESC) to run the filter as well. Even throttle output.

The reason to why the filter needs something to detect noise is because it needs to move with the motor frequency. The motors are the main source of noise and the filter needs to move with it. With rpm data, the filter knows at which Hz the motors generate noise and follows that. With throttle based it follows the throttle. Throttle based needs a bit more tuning since it initially won’t know where is should filter out noise, it just follows the throttle up and down.

The FFT is just one more way of giving the filter data to follow. The FFT measures actual noise and reports it to the notch filter which follows the noise. The filter settings will still need to be changed and tuned independently of the FFF settings to reach maximum effectivity.

I myself have used an FFT to drive the filters but now I’m using a 4in1 t-motor esc that has rpm telemetry. So I don’t need the FFT to run the filters.

Even though I don’t use the FFT to run the filters, I still have it enabled. This is because I can look at the FFT noise plot from the log. That way I can see the noise and I know if my rpm based filters are tuned property.

I hope I cleared some things out for you. I can be a bit unclear sometimes when I write but I hope this explanation works for you!