Smooth Scrolling is an experimental feature which aims to improve the responsiveness of scrolling and zooming for AVA documents. 

In previous versions high resolution displays had a slower response time, and this could affect the way scrolling appeared on the screen. In AVA 5.8 and higher, Smooth Scrolling will reduce the appearance of white squares when zooming, increase response time and smoothing animate colour changes. 

Smooth Scrolling is disabled by default but you can toggle it on and off by opening the AVA Settings > Display Settings > Enable Smooth Scrolling