In Ardour terminology, a <dfn>processor</dfn> is anything which treats the signal in some way and gets plugged into a mixer strip. Ardour provides several builtin processors such as the fader or panners. Processors can also be <dfn>plugins</dfn> used for effects or as instruments, as well as sends or inserts which affect <ahref="/signal-routing">signal routing</a>.
The arrangement of processors is arbitrary, and there is no limit to how many there can be. The Processor Box will automagically add a scrollbar to itself if there are more processors in it than can be shown in the given space.
The main box in the top half of a mixer strip shows the <dfn>processor box</dfn>. Processors are shown as colored rectangles, with a small "LED" beside them that lights up when the processor is enabled. The color of the processor depends on its location in the sequence; processors that are <dfn>pre-fader</dfn> are colored in red, and <dfn>post-fader</dfn> processors are colored green (in the default theme).
The <dfn>processor box</dfn> will always contain a blue <dfn>Fader</dfn> processor. This indicates where in the processor chain the main channel fader is located; this is the fader shown in the lower half of the strip. It can be enabled and disabled like any other processor.
Processors can also be dragged and dropped from the <ahref="/working-with-plugins/plugin-sidebar/"><dfn>Favorite Plugins</dfn> window</a> to an appropriate spot in the Processor Box.
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The <dfn>Favorite Plugins</dfn> window can be populated via the <ahref="/working-with-plugins/plugin-manager/">Plugin Manager</a>, or by dragging and dropping an existing processor from the <dfn>processor box</dfn> to the <dfn>Favorite Plugins</dfn> window.
Processors can be re-ordered using drag & drop. Dragging a processor allows it to be moved around within the chain, or copied to another processor list on another track or bus.
To the left of the name of each processor is a small LED symbol; if this is lit-up, the processor is active. Clicking on it will deactivate the processor and effectively bypass it.
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Some processors have their own bypass controls that are independent of the one that Ardour provides; this can make it appear that the plugin is non-responsive when its independent bypass control is active.
A processor in the <dfn>processor box</dfn> can be selected with a <kbdclass=mouse>Left</kbd>-click on it; it will be highlighed in red. Other processors can be selected at the same time by <kbdclass=mouse>Left</kbd>-clicking on them while holding down the <kbdclass=mod1n></kbd> key, and ranges can be selected by <kbdclass=mouse>Left</kbd>-clicking on them while holding down the <kbdclass=mod3n></kbd> key.
Context-click on the processor to be removed, and select <kbdclass="menu">Delete</kbd>; or <kbdclass=mod3n></kbd><kbdclass=mouse>Right</kbd>-click on it; or <kbdclass=mouse>Left</kbd>-click on it and press the <kbd>Delete</kbd> key. If multiple processors are selected, they will all be deleted at the same time.