11 Filter Graph Editor

11.1 Introduction

The filter graph editor allows complex signal processing pipelines to be developed in a graphical fashion. It may be accessed from the Window | Filter Graph menu item.

The graph editor view (Fig. 11.1) shows nodes for every instrument channel, trigger, and filter block in the current session. As new instruments, channels, and filter blocks are added to the session, new nodes will automatically appear in the graph editor view. Nodes cannot overlap and will automatically move out of the way if another node is dragged on top of them.

Fig. 11.1 Filter graph editor showing instrument channels and several processing blocks

11.2 Interaction

The view may be zoomed with the mouse wheel, or panned by dragging with the right mouse button, to navigate large filter graphs which do not fit on a single screen at a reasonable zoom level. Right clicking on a node opens a pop-up properties view (Fig. 11.2).

Fig. 11.2 Filter graph editor showing properties popup

Nodes display inputs at left and outputs at right. To connect two existing nodes, click on an input or output port and drag to the port you wish to connect it to. An input can only connect to one output at a time; if the destination already is connected to a different signal the previous connection will be removed and replaced with the new one.

A tooltip with a green plus sign is displayed during dragging if the proposed connection is valid. If the tooltip displays a red X instead, the connection is invalid (connecting two inputs, two outputs, or an input and output of incompatible data types).

To create a new node, click on an input or output port and drag to an empty area of the canvas (Fig. 11.3, Fig. 11.4). A context menu will appear, presenting a list of filters which can accept (if dragging from an output) or produce (if dragging from an input) the desired data type. If dragging from an input, the context menu will also include any currently unused instrument channels.

Fig. 11.3 Filter graph editor dragging from an output to an empty area of the canvas

Fig. 11.4 Filter graph editor dragging from an input to an empty area of the canvas

When a new node is added to the filter graph, each output channel will be automatically added to an existing waveform view if a compatible one is present. If no compatible view is available, a new view and/or group will be created.

Node title bars are color-coded to match the display color of the waveform trace, allowing easy navigation between waveform views and the graph editor.

Each node also includes a caption stating the type of node (hardware input, hardware output, or the name of the filter block) and, in most cases, an icon depicting the functionality of the block.footnote{Not all filters currently have icons. We are working with multiple artists to create more filter icons and welcome additional contributions.}

11.3 Grouping

In order to better organize complex experimental setups, nodes may be organized in groups. Groups cannot be nested.

To create a group, right click an unused area of the graph editor canvas and select New Group from the context menu. This will spawn a new, empty group near the mouse cursor position.

The group will have an automatically generated name (Fig. 11.5) by default. This name may be changed by right clicking on the group’s title bar and typing a new name in the pop-up.

Fig. 11.5 Newly created node group

To add a node to a group, simply drag the node by its title bar and move it into the group (Fig. 11.6). All paths from the node to the remainder of the filter graph will be routed through hierarchical ports at the left and right edges of the group, reducing clutter. Nodes may be freely moved around within the group to organize them, or dragged out of the group to remove them from the group.

A group (together with its contents) may be moved by dragging the group’s title bar with the left mouse button, or resized by dragging any of its corners. When a group is moved, it will push other nodes or groups out of the way to prevent overlapping.

If not needed, a group can be deleted by selecting it with the left mouse button and pressing the delete key. Deleting a group does not remove any nodes contained within it.

Fig. 11.6 Groups containing several nodes with hierarchical ports