Album Notes


Neural Synthesis

Disc 1:

Neural Synthesis No.6 (Binaural)

Neural Synthesis No. 7 (Binaural)

Disc 2:

Neural Synthesis No. 8 (Stereo)

Neural Synthesis No. 9 (Stereo)

This recording combines the art of music, the engineering of electronics, and the inspiration of biology. In it, David Tudor orchestrates electronic sound in ways analogous to our biological bodies' orchestration of consciousness.

The performance originates from a neural-network synthesizer conceived and built especially for David. He surrounds this synthesizer with his own unique collection of electronic devices, and in the recording on this CD made for headphone playback, he uses a new binaural technique for translating sound into out-of-head localizations in which sound seems to originate from specific, changing points within a space around the listener.

The concept for the neural-network synthesizer grew out of a collaborative effort that began in 1989 at Berkeley where David was performing with the Merce Cunningham Dance Company. I listened from the front row as David moved among interconnected electronic devices that filled two tables. He created a stream of remarkable sounds, overlaid them, filtered them, and fed them back upon themselves until the stream became a river. His attention moved from device to device, tasting and adjusting the mixture of sound like a chef composing a fine sauce of the most aromatic ingredients. I was spellbound. At the intermission I proposed to him that we create a computer system capable of enveloping and integrating the sounds of his performances.

We began meeting in New York to explore ideas. David had collaborated with a great many artists, scientists and engineers over the past decades to create performances on both an intimate and a grand scale. He put me in touch with many of them as our ideas took shape—people like John Driscoll, Phil Edelstein, Ron Kuivila, Billy Klüver, Max Neuhaus, Nic Collins, Lowell Cross, Carson Jefferies, Ivan and Serge Tcherepnin, Pauline Oliveros, Larry Shaw, Bob Bielecki, Bill Viola, Bill Hearn, Dana Massie, and—just months before their passing—John Cage and Fred Waldhauer. All of them contributed ideas enthusiastically. All said essentially the same thing about David's approach to music: he seeks to shape sound in all its dimensions, without limitation.

The unfolding of our ideas was an adventure in discovery and like all real adventures it led to unexpected places. What began as an effort to integrate the proliferation of electronic devices in David's performance environment ended in the addition of yet another device. In an early phase, Ron Clapman of Bell Labs and I explored designs using PBXs and pen-on-screen interfaces to switch a broadband matrix of analog and digital signals, including not only audio but video and performance-hall control signals. This led us to think about parallel processors with rich feedback paths.

In 1990, the project took a fundamental turn when I met Mark Holler from Intel at a computer architecture conference near Carmel, California. Mark was introducing a new analog neural-network microchip whose design he had recently managed. The chip electronically emulates neuron cells in our brains and can process many analog signals in parallel. It seemed a perfect basis for an audio-signal router, so I approached Mark with the idea during a walk along the Pacific coast beach. He thought it could work, offered a chip for experimentation, and we struck up an immediate friendship. Soon after, another colleague, Mark Thorson, joined us to work out the first hardware design for what was to become not only a signal router but also the analog audio synthesizer that David uses in this performance. Throughout our research and development, David provided a guiding light. His artistic intuition and his experience with electronic performance helped shape our thinking at each step.

The neural-network chip forms the heart of the synthesizer. It consists of 64 non-linear amplifiers (the electronic neurons on the chip) with 10240 programmable connections. Any input signal can be connected to any neuron, the output of which can be fed back to any input via on-chip or off-chip paths, each with variable connection strength. The same floating-gate devices used in EEPROMs (electrically erasable, programmable, read-only memories) are used in an analog mode of operation to store the strengths of the connections. The synthesizer adds R-C (resistance-capacitance) tank circuits on feedback paths for 16 of the 64 neurons to control the frequencies of oscillation. The R-C circuits produce relaxation oscillations. Interconnecting many relaxation oscillators rapidly produces complex sounds. Global gain and bias signals on the chip control the relative amplitudes of neuron oscillations. Near the onset of oscillation the neurons are sensitive to inherent thermal noise produced by random motions of electron groups moving through the monolithic silicon lattice. This thermal noise adds unpredictability to the synthesizer’s outputs, something David found especially appealing.

The synthesizer’s performance console controls the neural-network chip. R-C circuits, external feedback paths and output channels. The chip itself is not used to its full potential in this first synthesizer. It generates sound and routes signals but the role of learner, pattern-recognizer and responder is played by David, himself a vastly more complex neural network than the chip. During performances David chooses from up to 14 channels of synthesizer output, modifying each of them with his other electronic devices to create the final signals. He debuted the synthesizer at the Paris Opera (Garnier) in November 1992 in performances of Enter, with the Merce Cunningham Dance Company. In the 1994 recording for this CD, made during later experiments with the synthesizer in Banff, four discrete channels representing 12 recorded tracks are mixed to stereo.

Audio oscillators have a subtle but long history in Silicon Valley. Many local engineers date the beginning of the semiconductor industry to the 1938 development by Bill Hewlett and David Packard of their first product, an audio oscillator, in a downtown Palo Alto garage just a few blocks from the studio in which this synthesizer was built. Our work in 1993 and 1994 with David Tudor has led to the development, principally by Mark Holler, of a second-generation synthesizer built around multiple neural-network chips. It is a hybrid system using the analog neural-network chips to produce audio waveforms and a small digital computer to control neuron interconnections. The analog waveforms have frequency components ranging up to 100kHz and are much more complex than can be produced by a digital computer in real time. The performer will use the computer to change tens of thousands of interneuron connections during performance. The space of possible interneuron configurations is so large that it is difficult to reproduce the behavior of the synthesizer, which can evolve sound on its own over time. Searching for the regions of configurations that produce captivating sound becomes the challenge. It is possible that, with further development, the computer may be useful in finding these regions. Until then, there is no substitute for David.

The second synthesizer is still in its developmental stage. David and other colleagues continue their work with it. The recording on this CD presents the more mature first synthesizer. Its ability to generate captivating sound has become integral with David’s handling of it in so many live performances throughout the world.

      — Forrest Warthman, Palo Alto 1995

The Recording Process

David Tudor’s Neural Synthesis recordings are derived from an original score entitled Neural Network Plus. This piece was composed for and is performed by two musicians utilizing a 16-channel sound system with loudspeakers distributed throughout the performance space. The speakers are placed so that the performers can use the acoustic space as a musical tool. Producing a stereo recording of a piece like Neural Synthesis poses a challenge: how does one record and present this music without losing its musical and sonic integrity. Tudor’s music needs to be experienced by the listener in a way other than using the conventional two speaker stereo format.

A standard stereo recording presents music as a sound stage with a width limited by the separation of the speakers. (There are processes available that can expand the stereo image, however they pose strict listening constraints). Binaural recordings use the usual stereo format but with play-back over headphones, which allows spatial localizations encompassing a 360 degree circumference around the listener’s head. Sonically, the listener can perceive being in a space whether it be real, like the actual room in which it was recorded, or artificial, using electronic means to stimulate an environment. In this recording, David Tudor wished to utilize this technology to best represent all of the features of his music.

Neumann U87 microphones were placed on each of the 4 speakers oriented near the corners of the room. A stereo ambient microphone (Pearl TL-4) was placed in the middle of the room above a Sennheiser binaural head outfitted with Sony ECM-5 microphones. In addition, the direct signal from each of Tudor’s four mixer outputs was fed into the studio control room. Each of these signals were recorded onto 12 independent tracks of a Sony 3324 digital multi-track recorder.

Half hour performances were recorded without interruption allowing Tudor to formulate his material as he would in a live situation. A total of six “takes” were recorded onto the multi-track recorder.

Initially Tudor’s mix idea was to overlay two of the performance takes to essentially double the density of the musical material. He examined what musical material was used in each take and made decisions as to what takes would work well together, both musically and sonically. Upon experimentation he found that by simply overlaying one take with the other yielded an overly dense texture. Instead of simply combining two full mixes at equal level, one take was assigned the principal performance and mixed in its entirety. The second take was used only to embellish the principal mix.

In the stereo mix the principal mix was played back while the take chosen as the embellishing material was simultaneously mixed down. The secondary material was manipulated in response to what was happening in the principal mix, essentially rendering it a tertiary performance but with already performed material. Time delay-phasing techniques were used in the mixing process to create out-of-speaker localization effects dependent on where in the listening environment the listener resides.

In the binaural mix, the principal take was mixed down utilizing primarily the encoded tracks derived from the binaural head. This time, however, selected segments from the embellishing take were chosen for their interesting qualities and were in turn processed by 3-Space, a 3D localization algorithm. These segments were placed within the context of the principal mix so as not to disrupt its continuity

In both the binaural and the stereo mixes the material was combined digitally using a hard disk based work station.

      — John D.S. Adams, New York

In its design for live performance, Neural Synthesis relies upon an overlaying process exposing different levels of the source material. For this recording it was necessary to establish this process from the very beginning by utilizing multitrack technology. Successive performances were recorded and then mixed together enabling the exposure of different aspects of the material using varied modifiers.

It is the sum, the overlaying of the successive performances which establishes and defines the compositional process. As these recorded performances were approached as a compositional process, this is also how it needs to be listened to.

      — David Tudor, Stony Point, NY

In the world of American experimental music, David Tudor is something of a legend. For a number of years following the Second World War, he was the only performer to devote himself systematically to this music. In doing so, Tudor became a touchstone for some of the most radical musical activity of the 20th century. The praise accorded him by the composers whose music he performed attests to Tudor’s unique ability not only to meet the requirements of fully notated scores, but also to accomplish more than anyone had imagined in music in which some degree of indeterminacy was a compositional principle.

David Tudor was born in Philadelphia in 1926. He established himself as a pioneer in the performance of new music as early as 1950, when on December 17th, in New York, he gave the American premiere (and second performance anywhere) of the Second Piano Sonata of Pierre Boulez. From the early 1950s on, Tudor became John Cage’s closest associate. Cage stated that all of his works until about 1970 were written either directly for Tudor or with him in mind. Tudor also gave first or early performances of works by Earle Brown, Sylvano Bussotti, Morton Feldman, Karlheinz Stockhausen, Christian Wolff, Stefan Wolpe, and La Monte Young, among others. These composers often wrote works expressly for Tudor and a number of them stated that Tudor’s unerring ability to find his own imaginative and virtuoso solutions to the often puzzling and sometimes deliberately difficult problems of notation and performance was essential to the actual composition of their music.

In the late 1960s, Tudor gradually ended his active career as a pianist. He had begun to work with the electronic modification of sound sources in the late 1950s, departing from the then common practice of fixing music on magnetic tape. Instead, Tudor created electronic sounds directly during performances, thus pioneering what was later to be called “live electronic music.” By the mid-1960s, Tudor’s ideas and performances had inspired a new trend in electronic music. By the end of the decade, Tudor became fully involved in live electronic music, producing his own compositions using electronic technology.

As a composer, Tudor draws upon resources that are both flexible and complex. He uses, for the most part, custom-built modular electronic devices, many of his own design and manufacture. His compositional method employs musical as well as designing and manufacturing strategies. The choices of specific electronic components and their interconnections define each piece in both composition and performance. The music unfolds through large gestures in time and space, and many of Tudor’s works are associated with collaborative visual forces: light systems, dance, television, theater, film, or four-color laser production.

Tudor has been affiliated with the Merce Cunningham Dance Company since its inception in the summer of 1953. The Company has commissioned many works, including RainForest I (1968); Toneburst (1974); Phonemes (1981); Fragments (1984); Webwork (1987); and Virtual Focus (1990). Neural Synthesis (1992) was created for Cunningham’s Dance, Enter.

Several recordings of David Tudor’s music are available. “Tudor Plays Cage and Tudor” (Ear-Rational ECD 1039), contains Tudor’s 1982 recording of the Solo for Piano from Cage’s Concert for Piano and Orchestra, and his own Neural Synthesis (No.2), recorded in performance in March 1993. Microphone was released by the Italian label, Cramps, and Rainforest IV by the German Edition Block in collaboration with Gramavision, New York. Pulsers and Untitled are available on a Lovely Music LP.


3-Space is a binaural localization algorithm developed and written by Rick Bidlack at the Banff Center for the Arts. It allows dynamic, real-time control of the location of a sound source in a simulated three-dimensional space around the listener. Headphones are required for playback.

3-Space is implemented on the IRCAM Signal Processing Workstation (ISPW), a high-speed DSP board which resides in a NeXT host computer. It uses head-related transfer functions (HRTF’s) collected by Gary Kendall at Northwestern University, Evanston, IL.

Performed by David Tudor
Produced by David Tudor and John D.S. Adams
Recorded by John D.S. Adams with assistance from Roger Warnatsch
Mixed by John D.S. Adams
Digital Editing/Mixing: Roger Warnatsch
Assistant Engineer: Li Teo
Produced using the facilities of The Banff Center for the Arts: October/November 1993

Art Direction and Design: By Design

Partial funding for this recording has been provided by the Mary Flagler Cary Charitable Trust.

LCD 1602  [D] [D] [D]