Acoustical Society of America
Gold Medal Award - 1991

Manfred R. Schroeder

MANFRED R. SCHROEDER'S scientific accomplishments have influenced many areas of acoustics as evidenced by his more than 150 publications, 45 U.S. patents, and several published books, including, in 1991, his comprehensive Fractals, Chaos, Power Laws: Minutes From an Infinite Paradise (Freeman).

Manfred invented the voice-excited vocoder (VEV), the first vocoder that eschewed the customary electronic accent of synthetic speech.

Other fundamental contributions to speech include, in research with Bishnu Atal, linear predictive coding (LPC), which has become the method of choice for digital speech coding. His original proposal of spectrum shaping so that the quantizing noise is masked by the speech signal is now widely applied. By introducing the properties of the human ear into speech coders, high-quality speech at very low bit rates was achieved. His mathematical model with Joseph Hall of the inner-ear hair-cell response, based on release of neural quanta, stimulated both auditory modeling and physiological research.

Manfred's use of digital computers as signal generator and electronic filter allowed him, Gerhard Sessler, and James West to perform precise measurements, closely tailored to human perception, of the acoustical properties of Philharmonic Hall at Lincoln Center for the Performing Arts, New York, and other enclosures. They proved that integrating the squared impulse response of a linear network gives the average of infinitely many noise-excited decays in a single measurement. This is now a standard method for measuring reverberation time. Manfred's ingenious use of computer simulation of concert halls, either existing or planned, has had a profound effect on present concert hall design.

In electroacoustics, Manfred made use of digital computers for complex signal processing, which led to the ideas of employing allpass filters for artificial reverberation to minimize the coloration of reverberated signals. "Allpass reverberators'‘ are now in wide use. He also originated a method for converting a monophonic signal to "artificial stereophony," a method used in television to enhance sterophonic effects by widening the apparent sound base between closely spaced loudspeakers. Another of his electroacoustic invention is frequently shifting to improve the acoustic feedback stability of public address systems. His original research with Mohan Sondhi on the reconstruction of a two-dimensional object from its scattered sound field broadened the use of ultrasonics for medical imaging and other applications of nondestructive testing.

While still a student at Göttingen, Manfred used microwaves and electromagnetic cavities to investigate the distribution of resonances in rooms—including concert halls. In this connection he discovered the Wigner distribution of normal modes, which is now recognized as characteristic of nonintegrable ("chaotic") dynamical systems. Both his Ph.D. thesis and a subsequent theoretical paper on sound transmission in "large rooms" laid the foundation of a new field, based on the statistics of randomly interfering waves, characterized by a critical frequency, now called "Schroeder frequency," above which normal modes interact stochastically. These results are also important for coherent light and optical "speckles."

Manfred Robert Schroeder was born in Ahlen, Germany. In 1947 he began his studies at the University of Göttingen, where he obtained the degrees of Vordiplom in mathematics, and Diplom-Physiker and Dr.rer.nat. in physics.

In 1954 Manfred came to the United States to joint the research staff of Bell Laboratories, Murray Hill, New Jersey, where he first worked on speech analysis and synthesis. Together with Max Mathews, he was one of the leaders in the emerging art of computer simulation. In 1958 Manfred was appointed head of the acoustics research department at Bell and in 1963 he became director of the Acoustics and Speech Research Laboratory. In the following year he assumed responsibility for all areas of acoustics and ultrasonic research at Bell Laboratories.

In 1969 Manfred was appointed professor of physics and director of the Drittes Physikalisches Institut at the University of Göttingen, succeeding Professor Erwin Meyer. His work on concert hall acoustics, in collaboration with his students, resulted in the recognition of the importance of strong lateral sound waves for good acoustic quality. This evaluation of 20 major concert halls by direct auditory comparison, made possible by a new method of three-dimensional sound field reproduction, indicated a strong negative correlation between subjective preference and interaural similarity. Replying on his familiarity with number theory. Manfred showed how to construct phase gratings that scatter nearly equal energies into all diffraction orders to enhance lateral sounds in concert halls and recording studios. Such gratings are now available commercially for a variety of applications.

Professor Schroeder has been active in a number of projects for the U.S. government. He served on the National Stereophonic Radio Committee, an advisory group to the Federal Communications Commission, which formulated the standards for sterophonic broadcasting in the United States (now used throughout the world). He is a member of the Committee on Hearing, Bioacoustics, and Biomechanics (CHABA) of the National Research Council, and he served on the new Technologies Panel of the National Advisory Commission on Health Manpower. In 1963 he was a guest of the Soviet Government for consultation on the acoustics of the Palace of Congresses in the Kremlin.

Professor Schroeder is one of the pioneers in computer graphics, which continues to be one of his hobbies. In 1969 he was awarded the First Prize at the International Computer Art Competition for his application of concepts from mathematics and physics to the creation of artistic works.

Manfred served on the Executive Council of the Acoustical Society of America and as its Associate Editor for Speech. He is a fellow of the Acoustical Society of America, of the Institute of Electrical and Electronics Engineers, and of the Audio Engineering Society, which awarded him its Gold Medal in 1972. He is a member of the National Academy of Engineering and the New York and Göttingen Academies of Sciences, and a Fellow of the American Academy of Arts and Sciences. In 1975 he was appointed a foreign scientific member of the Max Planck Society. In 1987 the British Institute of Acoustics awarded him the Rayleigh Medal.

Manfred and his wife Anny continue to commute between their homes in Göttingen and Berkeley Heights, New Jersey. They relish bicycling and skiing on both sides of the Atlantic. Their daughter Marion is a neurologist and psychiatrist in Germany. Their son Julin is an assistant professor in biophysics at the University of California in San Diego, while their younger son, Alexander, at this writing, enjoys life as a ski instructor in Park City, Utah.

James E. West