The new GUI features new controls for added intuitivity and useability.

 The knobs

They are composed of a rotary knob controlled by the mouse (click on knob and move mouse forward/backward). They can also be controlled by keyboard when having input focus. This is shown with a light-blue circle surrounding the knob. The keys used are the arrow keys, page-up/page-down keys and the space bar.

The tickmarks around the knob can also be mouse-clicked to set the knob to related position directly. 

To set the knob to it's default value, just double-click on it, or press the space-bar when having input focus. As of yet the default value is non-configurable.

The buttons

They are  controlled by the mouse (just click on them). They can also be controlled by keyboard when having input focus. This is shown with a light-blue rectangle surrounding the button. The space-bar is then used to "press" the button.

The context menu

Not all programs allow you to select from the preset list (Logic Audio and Cubase VST for instance), so by clicking the right mouse button over Voice Tweaker, you'll bring up the context menu which will allow you to quickly choose a setting from the Voice Tweaker preset list.