It is now only available in the Brush Properties and Eraser Properties dialogs. The Centerline Smoothing slider has been removed from the Tool Properties view for the Brush and Eraser tool. It is possible that you are basing your need to use the Smoothing slider on how things performed in earlier versions and you may not have explored and fully recognized the enhancements. They describe the removal of the Smoothing slider as an “enhancement” in the Release Notes. Maybe Toon Boom decided that the enhancements in Harmony 17 reduced the need for the Brush tool Smoothing slider in the workflow and opted to streamline Tool Properties by removing that slider from the first layer of Tool Properties. The Centerline Smoothing slider is still present in that first layer of Tool Properties when using the Pencil tool. As far as I can tell there is no option to restore it to the first layer in Tool Properties. It had existed there and deeper within the editing tools and it still can be accessed there as you understand. The Smoothing slider for the Brush tool was removed from the Tool Properties front door level. This makes it impossible to create a brush that starts out with a very fine line with low pressure that can expand into a larger shape. The problem is, when I scale up the maximum slider, this also seems to scale up the size of the minumum brush size as well. It has built in stabilizing and smoothing enhancements. 1 In the bitmap brush settings we have a slider for ‘maximum size’ and ‘minimum size’.

You feel like you have a more responsive pencil or brush in hand as a result. When Harmony 17 was released there were significant changes made to the drawing engine which enhanced the experience. Many tutorials online were created using earlier versions of Harmony.

Toon boom harmony brush settings