Use Expression Controls effects to add a control that you can use to manipulate one or many properties’ values by linking the property to the control using expressions. A single control can affect several properties at once.

You can apply Expression Controls effects to any layer; however, it is useful to apply them to a null layer, which you can simply use as a controlling layer. You then add expressions to properties on other layers to take input from that control.

For example, you can add the Slider Control effect to a null layer (Null 1), and then apply this expression to the Position properties of multiple layers:

  position+[0,10*(index-1)*thisComp.layer("Null 1").effect("Slider Control")("Slider")]

In this example, as you drag the slider, each layer with this expression will move. The layers with greater index numbers (layers toward the bottom in the Timeline panel) will be shifted more than the layers with lower index numbers, at 10-pixel intervals. You can set keyframes for the slider on the null layer, and all of the other layers will animate accordingly.

You apply Expression Controls effects to a layer in the same ways that you apply other effects, such as dragging the effect onto the layer from the Effects & Presets panel.

Harry Frank shows how to use an Expression Controls effect (the Slider Control effect) as part of his video tutorial about converting from RGB to HSL using expressions: www.adobe.com/go/learn_ae_harryrgb2hsl.