An important aspect of any APB plug-in is that the plug-in is primarily a controller. The APB plug-in takes the input audio signal, combines it with a control signal, and sends both along a Thunderbolt connection to an APB unit for processing. The control signal sets up the analog components to do the selected algorithm with all the parameter values, and the audio signal is converted to the analog domain. The analog version of the audio signal is processed in the analog domain, and then converted back to the digital domain.

By operating the APB hardware from an APB plug-in in this way, all user controllable parameters are recallable and can be saved as presets. Furthermore, because the control signal is married to the input audio signal, parameters can be updating during playback with sample accurate automation.