OSC: Selection and Expansion Considerations

Ardour does not send every possible feedback value for each channel. It does send expanded information on the selected channel. There are also extra commands for the selected strip. All the feedback and select commands have their own path /select. This means that for the selected channel the surface does not have to keep track of the strip ID. The /select strip will follow the "current mixer strip" in the GUI editor window.

There are two major uses for this:

  1. Single strip control surfaces. Using /access_action Editor/select-next-route or /access_action Editor/select-prev-route to step through the mixer strips.
  2. Using a "Super strip" section of knobs to control parts of the strip that are changed less often such as polarity, sends or plugin parameters.

Selection in Ardour's OSC implementation are complicated by the possibility of using more than one OSC controller at the same time. User "A" may select strip 4 and use a selected controller to make changes to that strip. User "B" may subsequently select strip 7 to make changes on. This leaves user "A" making changes to strip 7 which they did not choose.

For this reason Ardour offers local expansion aside from the GUI selection. Local expansion only affects the one OSC controller. GUI selection is global and affects all controllers using GUI selection as well as the GUI.

Both select and expansion use the /select set of commands.

In general, in a one user situation where that one user may use either the OSC surface or the GUI, using GUI based selection makes the most sense. This is the default because this is the more common use.

When there is more than one operator, then expansion only is the mode of choice. It may make sense for one of the surfaces to use GUI selection where the operator is also using the GUI for some things. However, the set up should be carefully analyzed for the possibility of selection confusions. Expansion should be considered the safe option.

It is always ok to use expansion on the surface even in a one user scenario. This allows the user to use GUI and surface selection for different uses.

It is also possible to use both if desired. /strip/select will ways set the GUI select, but /strip/expand will set the select feedback and commands locally without changing the GUI select. Another /strip/expand or a /strip/select will override that expand command and releasing the /strip/expand or /select/expand (setting it to 0 or false) will set the /select set of commands and feedback back to whichever strip the GUI has selected at that time. This could be used to switch between the GUI select and the local expand to compare two strips settings.