Realtime Control of Audio Effects

Søren H. Nielsen
DAFx-1999 - Trondheim
Many sound processing effects need or can benefit from realtime control of one or more parameters. During interaction with the processor optimum settings can be achieved, or settings can be signal dependent. Time variance is a keyword here. For some effects the routing and mapping of the controller signals is of higher complexity than the audio signal routing itself. A concept for controlling a collection of effect blocks in real time with direct user interaction, and including controllers derived from the signal itself, is presented. This consists of a hierarchy of physical controllers, logical controllers, connection matrix, mapping functions, and effect parameters. And below that an effect parameter often controls several parameters in the signal processing algorithm. One controller can control more than one parameter and the mapping function from controller to the parameter can be set individually. Making this very flexible system easy to use presents some interesting challenges for the user interface design. Furthermore, as control signals can be derived from the audio signal itself, the signal processor has to calculate parameters from controller settings to a much higher extent than typically done, when a host processor takes care of this. The concept has been implemented in commercially available stand-alone effects processors.