Tactus addresses problems of synchronizing and controlling various interactive continuous-time media. The Tactus system consists of two main parts. The first is a server that synchronizes the presentation of multiple media, including audio, video, graphics, and MIDI, at a workstation. The second is a set of extensions to a graphical user interface toolkit to help compute and/or control temporal streams of information and deliver them to the Tactus Server. Temporal toolkit objects schedule computation events that generate media. Computation is scheduled in advance of real time to overcome system latency, and timestamps are used to allow accurate synchronization by the server in spite of computation and transmission delays. Tactus supports precomputing branches of media streams to minimize latency in interactive applications. KEYWORDS: interface, toolkit, multimedia, synchronization, interactive, realtime 1 Published as: Dannenberg, Neuendorffer, Newcomer, and Rubine, "Tactu...

Canon is both a notation for musical scores and a programming language. Canon offers a combination of declarative style and a powerful abstraction capability which allows a very high-level notation for sequences of musical events and structures. Transformations are operators that can adjust common parameters such as loudness or duration. Transformations can be nested and time-varying, and their use avoids the problem of having large numbers of explicit parameters. Behavioral abstraction, the concept of making behavior an arbitrary function of the environment, is supported by Canon and extends the usefulness of transformations. A non-real-time implementation of Canon is based on Lisp and produces scores that control MIDI synthesizers. Introduction Canon is a computer language designed to help composers create note-level control information for hardware synthesizers or synthesis software. Canon was motivated by my need for a simple yet powerful language for teaching second-semester stud...

:W is a systematic approach toward the construction of event-driven, interactive, real-time software. W is driven by practical concerns, including the desire to reuse existing code wherever possible, the limited real-time software support in popular operating systems, and system cost. W provides a simple, efficient, software interconnection system, giving objects a uniform external interface based on setting attributes to values via asynchronous messages. An example shows how W is used to implement real-time computer music programs combining graphics and MIDI. 1. Introduction Real-time interactive music systems are among the most demanding computer applications. In addition to the usual algorithm, data structure, and implementation problems, interactive music systems must respond to input in milliseconds and deal with a variety of input and output media. Special structures are required to satisfy these real-time requirements, leading to programming styles not supported by ordinary sof...

The development of broadband ATM networking makes it attractive to use computer communication networks for the transport of digital audio and motion video. Coupled with advances in workstation technology, this creates the opportunity to integrate these continuous information media within a distributed computing system. Continuous media have an inherent temporal dimension, resulting in a set of synchronisation requirements which have real-time constraints. This dissertation identifies the role and position of synchronisation, in terms of the support which is necessary in an integrated distributed system. The requirements for synchronisation are divided into two categories. Stream synchronisation is concerned with issues such as delay jitter with respect to the presentation of a single continuous media stream, as well as maintaining the relationships which may exist between multiple streams. Event synchronisation allows applications and system services to co-ordinate their behaviour bas...

: Operating systems are often the limiting factor in creating low-latency interactive computer music systems. Real-time music applications require operating system support for memory management, process scheduling, media I/O, and general development, including debugging. We present performance measurements for some current operating systems, including NT4, Windows95, and Irix 6.4. While Irix was found to give rather good real-time performance, NT4 and Windows95 suffer from both process scheduling delays and high audio output latency. The addition of WDM Streaming to NT and Windows offers some promise of lower latency, but WDM Streaming may actually make performance worse by circumventing priority-based scheduling. 1. Introduction A modern CPU can run extensive and sophisticated signal processing faster than real time. Unfortunately, executing the right code at the right time and performing time-critical I/O may very well exceed the capabilities of a modern operating system. Latency i...

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ly, there is a mathematical function that maps beat numbers to time and an inverse function that maps time to beats. (Some special mathematical care must be taken to allow for music that momentarily stops, instantaneously skips ahead, or is allowed to jump backwards, but we will ignore these details.) One practical representation of the beat-to-time function is the set of times of individual beats. For example, a performer can tap beats in real time and a computer can record the time of each tap. This produces a finitely sampled representation of the continuous mapping from beats to time, which can be interpolated to obtain intermediate values. MIDI Clocks, which are transmitted at 24 clocks per quarter note, are an example of this approach. The Mockingbird score editor [Maxwell 84] interface also supported this idea. The composer would play a score, producing a piano-roll notation. Then, downbeats were indicated by clicking with a mouse at the proper locations in the piano roll score....

Digital interactive media augments interactive computing with video, audio, computer graphics and text, allowing multimedia presentations to be individually and dynamically tailored to the user. Multimedia, and particularly continuous media pose interesting problems for system designers, including those of latency and synchronization. These problems are especially evident when multimedia data is remote and must be accessed via networks. Latency and synchronization issues are discussed, and an integrated system, Tactus, is described. Tactus facilitates the implementation of interactive multimedia computer programs by managing latency and synchronization in the framework of an object-oriented graphical user interface toolkit. 1. Introduction High-bandwidth digital communication is creating many new possibilities for interpersonal and human-computer interaction. An important dimension of the new technology is the ability to transmit multimedia information, information that engage...

Aura is a sound synthesis engine built on top of W, a real-time message-passing object system.

The programming language Arctic specifies real-time behavior declaratively by using temporal control constructs and by indicating starting times and durations explicitly, much the way timing is specified in a cue sheet or a musical score. Values in Arctic are functions of time, which may be combined with various arithmetic and logical operators. Since Arctic is a single assignment language, the execution order is implied by data dependencies, simplifying synchronization problems for the programmer. Arctic supports behavioral abstraction, in which a single program module gives rise, through various transformations, to a class of behaviors. An implementation of Arctic is described, and experience with the declarative approach to real-time control is discussed. 1. Introduction For the most part, traditional programming languages have been designed for applications where control over the timing of execution is not a primary concern. Users usually want their programs to run as fast as poss...