Edgar Berdahl

Satellite CCRMA: A Musical Interaction and Sound Synthesis Platform

This paper describes a new Beagle Board-based platform for teaching and practicing interaction design for musical applications. The migration from desktop and laptop computer-based sound synthesis to a compact and integrated control, computation and sound generation platform has enormous potential to widen the range of computer music instruments and installations that can be designed, and improves the portability, autonomy, extensibility and longevity of designed systems. We describe the technical features of the Satellite CCRMA platform and contrast it with personal computer-based systems used in the past as well as emerging smart phone-based platforms. The advantages and trade-offs of the new platform are considered, and some project work is described.

Advancements in actuated musical instruments

This article presents recent developments in actuated musical instruments created by the authors, who also describe an ecosystemic model of actuated performance activities that blur traditional boundaries between the physical and virtual elements of musical interfaces. Actuated musical instruments are physical instruments that have been endowed with virtual qualities controlled by a computer in real-time but which are nevertheless tangible. These instruments provide intuitive and engaging new forms of interaction. They are different from traditional (acoustic) and fully automated (robotic) instruments in that they produce sound via vibrating element(s) that are co-manipulated by humans and electromechanical systems. We examine the possibilities that arise when such instruments are played in different performative environments and music-making scenarios, and we postulate that such designs may give rise to new methods of musical performance. The Haptic Drum, the Feedback Resonance Guitar, the Electromagnetically Prepared Piano, the Overtone Fiddle and Teleoperation with Robothands are described, along with musical examples and reflections on the emergent properties of the performance ecologies that these instruments enable. We look at some of the conceptual and perceptual issues introduced by actuated musical instruments, and finally we propose some directions in which such research may be headed in the future.

Feedback control of acoustic musical instruments: Collocated control using physical analogs

Traditionally, the average professional musician has owned numerous acoustic musical instruments, many of them having distinctive acoustic qualities. However, a modern musician could prefer to have a single musical instrument whose acoustics are programmable by feedback control, where acoustic variables are estimated from sensor measurements in real time and then fed back in order to influence the controlled variables. In this paper, theory is presented that describes stable feedback control of an acoustic musical instrument. The presentation should be accessible to members of the musical acoustics community who may have limited or no experience with feedback control. First, the only control strategy guaranteed to be stable subject to any musical instrument mobility is described: the sensors and actuators must be collocated, and the controller must emulate a physical analog system. Next, the most fundamental feedback controllers and the corresponding physical analog systems are presented. The effects that these controllers have on acoustic musical instruments are described. Finally, practical design challenges are discussed. A proof explains why changing the resonance frequency of a musical resonance requires much more control power than changing the decay time of the resonance.

The firefader: Simple, open-source, and reconfigurable haptic force feedback for musicians

The FireFader is a simple haptic force-feedback device that is optimized for introducing musicians to haptics. It is based upon a single-degree-of-freedom potentiometer fader coupled to a DC motor, also known as a “motorized fader.” A light is connected in parallel with the motor to help communicate the forces strength visually. The FireFader consists of only open-source hardware and open-source software elements. Consequently, it is relatively easy for users to repurpose it into new projects involving varying kinds and numbers of motors and sensors. An open-source device driver for the FireFader allows it to be linked to a computer via USB so that the computer can perform the feedback control calculations. For example, the computer can simulate the acoustics of a virtual musical instrument to concurrently synthesize sound and calculate the motor force as a function of the fader position. The serial connection over USB increases the latency of the control signal compared to embedded implementations, but the serial connection facilitates easier programming via the computer, and the force feedback can be automatically disabled when the user is not touching the fader. Some new devices derived from the FireFader design are presented.

Force-Sensitive Detents Improve User Performance for Linear Selection Tasks

Haptic technology, providing force cues and creating a programmable interface, can assist users in more accurately using an interface. This paper investigates haptic assistance in combination with auditory feedback instead of visual feedback. A user test is carried out in which participants select fundamental frequencies from a continuous range to play brief musical melodies. Two control conditions are compared with two detent-based haptic assistance conditions. The detents gently guide the users toward locations of equal tempered fundamental frequencies. Results from the user test confirm improved accuracy brought about by the detents. It is further helpful to provide regulation of the strength of haptic assistance in real time, allowing the user to remain always in control. This concept motivated the force-sensitive detent condition, which enables the user to adjust the strength of the haptic assistance in real time by changing the downward force applied to the haptic device. The work implies that users of graphical user interfaces could similarly benefit from force-sensitive detents and more generally real-time regulation of the strength of haptic assistance.

Active control of a vibrating string

We discuss the specifics of applying active feedback control to a vibrating string. Using sensors, actuators, and digital controller hardware, we make the acoustics of the string programmable, yet the string retains its tangible qualities. As a consequence, fretting, bowing, and plucking controlled and uncontrolled strings have similar physical consequences. Consider that any controller emulating a network of springs, masses, and dashpots attached to the string is a passive controller. To allow the strings acoustics to be programmable over a wide range, we should be able to implement passive controllers. This means that there must be at least one linear and collocated sensor/actuator pair. We explain how to construct such a pair in the laboratory. Finally, we explain one controller particular to one‐dimensional systems such as vibrating strings. Whenever the sensor detects a pulse arriving, the actuator emits a new pulse. The output spectrum consists of a harmonic series proportional to the sampling of t...

Tangible embedded Linux

During this studio, participants will learn about tangible embedded Linux and how to harness it for building durable, living prototypes. By the end of the studio, each participant will complete a simple tangible prototype using the Satellite CCRMA kit, which is about twice the size of a deck of cards. Satellite CCRMA is currently based on the powerful Raspberry PI embedded Linux board, which executes floating-point instructions natively at 700MHz. Participants will be led through running Pure Data (pd) on the board, but participants are welcome to explore other software available on the Satellite CCRMA memory image. Additional topics include Arduino, Firmata, pico projectors, open-source hardware, and more.

Applications of passivity theory to the active control of acoustic musical instruments

The dynamic behavior of any acoustic musical instrument can be modified by closing a feedback loop around even a single sensor and actuator. The ultimate goal is to make the acoustics of the instrument programmable by way of a digital feedback controller, while the instrument retains its tangible form. In this talk, we describe a class of controllers that are applicable to passive acoustic musical instruments, and we present sound examples from laboratory experiments on a vibrating string. First, we briefly introduce positive real functions. Next, we design positive real controllers allowing the quality factor and resonant frequency of instrument modes to be individually controlled. Because positive real controllers are passive, they are stable if the instrument is passive. This means that neither a full instrument model nor complete state measurements are required. Finally, we describe a class of simple passive nonlinear controllers that can emulate various kinds of friction, stiffening and softening springs, etc. Passivity of these controllers follows from the local passivity of the controller components. Controller parameters may often be tweaked so that the controllers are no longer passive but still perform useful functions, such as bowing emulation.

Hybrid Virtual Modeling for Multisensory Interaction Design

The Synth-A-Modeler compiler enables portable, rapid and modular prototyping of audio-haptic models for single degree-of-freedom (d.o.f.) haptic interaction. This paper introduces hybrid modeling in Synth-A-Modeler, which mixes traditionally disparate virtual modeling paradigms from the computer music literature: digital waveguide models, mass-interaction models, and modal synthesis models. Hybrid modeling enables more salient adjustment of model parameters. Using the open-source Synth-A-Modeler toolchain, the resulting models can be compiled for a wide variety of programming languages and haptic devices, and the models are made openly available to the research and music communities.

Electroacoustics laboratory assignments for computer music students

A series of pedagogical exercises are described that integrate concepts from traditional musical acoustics laboratory assignments with the fundamentals of computer music. Students are asked to rapidly prototype hybrid devices that contain both musical acoustic components as well as sensors, embedded audio signal processing, and loudspeaker drivers. To help students rapidly complete working prototypes, students are provided with working audio effects and sound synthesizer programs. Students learn the programming language (Pure Data) only by example for making small changes to the previously designed programs, as they are integrated with custom-made, physical acoustics components (e.g., D-I-Y vibrating strings, drums, columns of air, rattles, etc.). Music students first learned that building quality acoustic instrument components is harder than they originally thought. Although out-of-the-box thinking is regarded as an important factor in devising novel electroacoustic prototypes, students starting from pre...