A Short History of Digital Sound Synthesis by Composers in the U.S.A

A Short History of Digital Sound Synthesis by Composers in the U.S.A. Chris Chafe Center for Computer Research in Music and Acoustics (CCRMA) Department of Music, Stanford University Stanford, California 94305 [email protected] Abstract: A new technology for music has emerged with unprecedented speed. Just over forty years ago, the first digitally-produced sounds gave pioneering composers from around the world a taste of vast new possibilities. Numerical experiments with sound became a logical extension of compositional interests that were pushing the boundaries of timbre, perception, new instruments and performance techniques, organization and paradoxically, indeterminism. At several centers including a small number in the U.S. interdisciplinary teams combined composition with research in musical acoustics, psychoa- coustics, and artificial intelligence. Their musical works provide a timeline of progress in sound synthesis. converters for sound acquisition and playback, but the promise was already apparent when a 1. Introduction "Portrait of the Computer as a Young Artist” was published: To describe the past four decades in a nutshell, we see composers, scientists, and engineers Today, scientists and musicians at MIT, working to develop a new musical medium; ex- Bell Telephone Laboratories, Princeton ploring the fabric of sound and sound perception; University and the Argonne National and pushing a new technology's scale and capa- Laboratory are trying to make the com- bilities rapidly towards the practical and effec- puter play and sing more surprisingly and tive. Briefly looking forward another stretch of mellifluously. As a musical instrument, time, this same description might apply to music the computer has unlimited potentialities made using direct stimulation of auditory sensa- for uttering sound. It can, in fact, pro- tions in the brain. Far fetched? Brain imaging duce strings of numbers representing any techniques that are central to perceptual studies conceivable or hearable sound… Won- suggest such a possibility. Magnetoencephalo- derful things would come out of that box graphy (MEG) shows promising temporal and if only we new how to evoke them. spatial resolution for music, perhaps foreshad- [Pierce 1965] owing the analytic side of this futuristic medium. And its synthetic reverse, transcranial magnetic The timeline of compositions below follows the stimulation (TMS), though still quite course, has development of synthesis algorithms along such a been used to induce certain non-auditory effects. track, citing several examples of new techniques Electrical stimulation of the inner ear is already which replicated observed patterns and musical in prosthetic use. In time, consequent technolo- signals, and which were rapidly incorporated in gies may lead to an evoked music (I’m just hoping composers’ work. The compositions described are for early work on the problem of loudness con- the fruits of research into new materials: they trol). engage the listener in a completely illusory world which could only have been achieved with digital Presently, about sixty sites are equipped for MEG 1 analyses and a handful for experimentation with tools. TMS. My prediction is that just as with digital sound synthesis over forty years ago, at some point an observed auditory pattern will be syn- 1 Listening to the accompanying, brief musical thetically induced and from then a new medium excerpts and explanatory sound examples will for composers will be born. Rewinding to 1965, enhance an appreciation of the timeline (total there were likewise only a few sites equipped duration is about 20 minutes). Each work consti- with computers and the necessary digital audio tutes a waypoint in a list that is much longer than Wendy Carlos’ album Switched on Bach. A Composers were immediately attracted by a gen- newer technology often invites its usage for imi- eral-purpose machine which by itself prescribes tation of the sound of an earlier technology. This no particular musical style, but which must be fed cascade leads right to the present were we can models and insights to produce results. Solutions even hear digital software imitating analog hard- which seem logical to us with hindsight were ware imitating mechanically-produced sound. gained through key advancements in the under- standing of the materials and nature of music. Models employed in the compositions cited be- “Musical Sounds from Digital Computers” in the low fall into five general categories: contemporary music journal, Gravesaner Blätter, • closed with: subtractive acoustical models (beginning with source / filter vocal simulations) The Future of Computer Music • additive acoustical models (recreating Man’s music has always been acousti- Fourier analyses) cally limited by the instruments on which he plays. These are mechanisms which • impulsive linear physical models (beginning have physical restrictions. We have made with plucked string simulations) sound and music directly from numbers, • self-sustained physical models with acousti- surmounting conventional limitations of cal feedback (electric guitar simulations with instruments. Thus the musical universe is feedback) now circumscribed only by man’s per- ceptions and creativity. • self-sustained physical models with non- linear excitation (beginning with simulations [Mathews 1962] of bow, reed and air jet) And more from Pierce’s “Portrait:” In each case, a good dosage of acoustical theory The computer is a great challenge to the and analysis of existing instruments provided the artist. It enables him to create within any platform upon which the modeling approach was set of rules and any discipline he cares to developed. communicate to the computer. Or, if he abandons discipline, he may leave eve- rything to chance and produce highly ar- 2.1. Acoustical tistic noise. Acoustical models involve spectral (frequency This is an attempt to portray the rapid progress domain) descriptions of patterns of air pressure and excitement which began to fill that vast po- variation radiated by the modeled instruments. tential enabled by digital tools. The most common is based on Fourier analysis in which an acoustical wave, picked up by micro- phone, is analyzed to give an accurate portrait of 2. Modeling its time-varying spectral components. Identical components are generated digitally and become For many disciplines, music included, the digital sound again via loudspeaker. Ideally, if the signal computer has enabled the age of modeling. The can be adequately analyzed, the resulting model arsenal of techniques for numerical simulation of will enable high quality resynthesis, as well as a natural phenomena (including for example, be- large set of transformations. havior of a trumpet) continues to expand with Acoustical models can also be based in analysis addition of new models expressed as algorithms of hearing, supplying those cues known to en- and / or data sets from analysis. In all forms, they voke a particular musical or auditory sensation. can be studied under different hypothetical con- Such sounds might not be based in the real world ditions, from the plausible to the extreme. at all, and are instead formulated from psychoa- Imitative synthesis of musical sounds is an old coustical principles or paradoxes. tradition and spans the major epochs of technolo- gies, including mechanical organs with stops like the vox humana, or analog electronic synthesizers 2. 2. Physical with patches like the instruments played on Physical models describe the vibrating mechanisms of (instruments and other) sound sources. what is represented. Many others (in the U.S. and Analysis and synthesis is either in the time do- internationally) have contributed to the medium main, in terms of mechanical or fluid dynamics, and their music could be included, but then this or in the frequency domain, as mixtures of dis- wouldn’t be a short history. tinct modes and regions of vibration. numbers alone represents a great technical step. It Dynamics-based modeling has not yet gained a required development of software with musically- general-purpose analytic method. Synthesis mod- useful frequency and dynamic ranges and that els are constructed by capturing “first principles” handed over to the machine a certain amount of of a physical system and then refining the model sonic detail. Without the latter, the composer by addition of physical details that are perceptu- would be lost in a sea of numbers. It marks the ally significant. The resulting sonic advantages, beginning of a medium in which software is di- particularly with regard to transients and long- vided into two layers, one for the generation of term laws (e.g., connected note transitions, tur- sounds as notes (coded as sound-producing sub- bulence or timbre control spaces), often remain routines) and the other a list of the notes to be outside the present powers of analysis for acousti- played (as calls on the subroutines). Since then, cal models. almost ubiquitously, the parameters compiled into A very young field at the moment ties physical note lists have indicated timing, pitch, loudness, modeling in with research in hearing: are there and aspects of timbre. effects similar to those in acoustically-described perceptual illusions that can be expressed in terms of the physics of the sound source itself? If so, 3.2. (1961) Hal’s Tune this may lead to a new class of physical models Mathews arranged Bicycle Built for Two using rooted in sensation rather than real-world simula- waveform techniques and J. Kelly's vocal tract tions. analog speech synthesis approach (a physical simulation of the shape of the vocal tract using a series of continuously changing digital filters). 3. Bell Labs Experiments The resulting performance became a well-known performance of the traditional song having been The very first examples of digital sound synthesis incorporated by the creators of the movie, 2001: were created alongside research in speech tech- A Space Odyssey. Hal, the computer, sings this nology. Though the computer hardware was the excerpt as his memory is removed bit-by-bit. same, new software was needed to meet the re- quirements of musical sound generation and organization.

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