Control Structure and Parameter Distribution

While the audio processes included in an augmented performance system can vary widely and will contribute fundamentally to the sonic quality and scope, any design will rely on an accessible control structure, unless more compositional approaches of sequenced or generative structures are employed. At first it might appear desirable to allow convenient access to every parameter available in the system. The previous discussion on operational and performative activity has already indicated that such an approach might have a negative impact on the flow of a performance, as audible changes to processes might require adjustments of several parameters (operational tasks) to invoke a single intended change in the music. Not all electroacoustic processes can be controlled as effectively with a single performative gesture as the example of the filter sweep executed with a single controller (i.e. MIDI fader). The implementation and use of controllers has a direct relationship to the musical outcomes. Implementing direct control for every (or at least every musically significant) parameter allows maximum of adjustability, but might impact the practicality and performability of the system. MIDI controllers are easily implemented for direct controls for specific parameters. Custom build controllers137_{, optimising the layout design of the controls, might be developed as} instruments in their own right138 _{or improve use in combination with acoustic} instruments.

A slightly different approach is apparent in works focusing on sensors to capture performance gestures: In order to avoid designing a system which requires additional control activity, the gestures of playing the acoustic instrument are tracked and its data interpreted in order to generate relevant control of the electronics. These “indirect controllers” intend not to disturb any performance activity on the acoustic instrument 137 _{E.g. The Hands by Michel Waisvisz 1984, 1989, 2005.}

138 _{Soundbeam (http://www.soundbeam.co.uk), Haken Continuum (http://www.hakenaudio.com/Continuum/),}

Nick Francis’ Choppertone (http://www.ableton.com/choppertone), Eigenharp by Eigenlabs (http:// eigenlabs.com ).

and also to allow the use of gestures akin to those used on the instrument (i.e. bowing gesture in the air rather on the string).

“Direct control” and “indirect control” is proposed as an useful differentiation of implemented controllers: “Direct controls” enable intensional changes of parameters for either operational or performative control gestures. The change of volume of the electronics with a fader is a prime example of direct control. The physical movement of the fader has an immediate effect on the parameter. Envelop following, using analysis to side-chain volume changes of a sound in dependence on the amplitude of another, is an example for indirect control. Here it is possible to generate data from performance gestures and apply these to other parameters.

When different audio sources (array of different microphones and pickups) are used with a number of effects, additional control demands arise to establish signal routing. This can be addressed by either hardwiring specific audio inputs to certain effects, or allowing a flexible system. The most flexible system obviously allows real-time changes to patch any of the microphones to any effect. Also, a dynamic routing system of the effects to the system output or to serve as the source for another process can be beneficial. These decisions on the signal routing and the serial or parallel use of effects determine the possibilities of the electronically enhanced system and indicate that the program design is a form of composition. Fixed signal routings will suffice for programs designed for a specific musical composition or a particular approach to a musical realisation, as it can be assumed that the design reflects the musical concern/ interest when it was written.139 _{A concern maintaining instrumental potential for a wider} context favours more flexibility, in its extreme, to allow any decision about the signal routing during performance. For example, changing the input for a ring-modulator from a pickup to an air mic shifts the focus of a very isolated sound source to open the possibility to consciously work with the room resonances and feedback. It also might affect the whole ensemble as the sounds of other players bleed into the microphone. Similar flexibility might be desired for the control structure of parameters. Different musical scenarios might impose different requirements to control the system. Because discrete direct controls for every parameter might create cumbersome operation during 139 _{A ‘composition’ which does not prescribe musical outcomes and realisations, but outlines the musical}

performance, grouping several parameters to a single controller can feel more natural. “Divergent mapping”140 _{strategies also allow parameter changes to be designed in more} complex ways. For example, while one parameter is controlled linearly, another might be changed anti-proportionally, exponentially or according to algorithms. It is aimed that the position of the controller sets specific constellations and mixes of the available processes and that the movement of the single controller allows quick and intuitive control of the processes. The very recent release of SugarBytes Turnado plugin141 _shows an interesting commercial application of this approach, exceeding the possibilities of the slightly more common preset morphing available in some commercial plugins142_{. The} practicality of this method is undisputed, as it allows quick and complex changes with minimal operational tasks. However, implementations of divergent mapping reduce the flexibility of adjusting the system during performance. The distribution curves and parameters have to be designed prior to performance in relation to successful sonic outcomes. It can be a time consuming process and impractical to be changed on stage, unless the performer has the possibility to switch between presets of divergent distributions adequate for different musical situations.

“Convergent mapping” 143 _{strategies add the possible data distribution where one} controller’s range is dependent on another. I.e. the fader controlling ring-modulation would enact different values according to the position of a second. This is a particularly interesting scenario, as for example data streams of indirect controllers such as from sensors or audio analysis can have more or less impact on the process dependent on a single direct controller.144

The possibilities and complexities of the parameter routing are unlimited, but any design appears to have consequences for the performance. It can be assumed that every composer and performer has engaged with these issues in one form or another and solutions can be very individual. While some might prefer to work with fixed media 140 _{Hunt 2000.}

141 _{SugarBytes’ Turnado (http://www.sugar-bytes.de/content/products/Turnado/index.php last visited}

20.07.2012) appears to be the most sophisticated commercially available tools to date, allowing complex divergent effect mapping in the implemented Director.

142 _{GRM tools (http://www.avid.com/US/products/GRM-Tools-Classic), Flux plugins (http://flux-}

home.com last visited 20.07.2012) .

143 _{Hunt 2000.}

144 _{Using a fader to change the degree of ring-modulation invoked on the audio signal, i.e. fader value 0%}

would result in a fixed modulation frequency, 100% would open the amplitude reading to change the modulation frequency according to the loudness of the sound.

playback as the electronic parts would require sophisticated control structures they do not have available to them, others might design structures which enable a selected range of controllers or control data streams to control different parameters during the performance of compositions according to time-lines145 _{or score following}146_{. The idea} to retain a more universal instrumental approach by designing a more flexible system which makes processes available for an augmented instrument is challenging. A possible approach is proposed below as the piano+ incorporating a mixture of these approaches and is described in more detail in Chapter 4.