Internationally known acoustician Manfred Robert Schroeder died at his home in Göttingen, Germany, on 28 December 2009 after a brief illness. He was renowned for his work in such diverse fields as speech synthesis, architectural acoustics, computer art, and number theory.

Manfred was born on 12 July 1926 in Ahlen, Germany. He studied mathematics and physics at the University of Göttingen and received his doctorate for his thesis on the distribution of acoustic normal modes in enclosures as a student of Erwin Meyer in 1954. Later that year he joined Bell Labs in Murray Hill, New Jersey; he was appointed head of the acoustics research department in 1958 and director of the acoustics and speech research laboratory in 1963. Soon thereafter he assumed responsibility for all areas of Bell’s acoustics, ultrasonics, and mechanics research.

In 1969, still maintaining some of his responsibilities at Bell Labs, Manfred was appointed professor of physics and director of the Third Institute of Physics at the University of Göttingen. After retiring from his positions at Bell Labs and the university in 1987 and 1991, respectively, he continued his activities as a scientist and teacher until shortly before his death.

One of the fields Manfred was always enthusiastic about was room acoustics, to which he made many fundamental and far-reaching contributions. The area had already fascinated him during his thesis work. In later publications he described the relations between the eigenmodes and the frequency response of rooms and explained the random character of the response above a certain frequency, today known as the Schroeder frequency.

Other ingenious contributions to room acoustics followed. Among them were the integrated-tone-burst method for measuring reverberation times of enclosures and the use of frequency shifting to suppress feedback in public address systems. Another outstanding achievement is Manfred’s invention of pseudo-random surface structures, or Schroeder diffusers, based on number-theoretical schemes. Such devices scatter sound waves in all directions to provide lateral sound reflections and thus improve the acoustics of concert halls.

Receiving great public interest was Manfred’s involvement in activities to improve the acoustics of Philharmonic Hall (now Avery Fisher Hall) in New York City’s Lincoln Center. Soon after the hall opened in 1962, musicians, conductors, and music critics detected grave deficiencies in its acoustics. Asked along with other acoustic consultants to objectively evaluate the acoustics, Manfred used a novel measuring method based on digital signal generation and processing. Preparation, performance, and evaluation of the experiments turned into a scientifically challenging project for him and his coworkers. Later, while in Göttingen, Manfred and his students evaluated 20 of the world’s major concert halls by subjective auditory comparison, and in the process they gathered significant information about lateral reflections and other acoustic parameters. Apart from the new digital measuring techniques, Manfred developed versatile computer simulation methods for large halls. His methods have become increasingly important in the planning of new auditoriums.

Manfred was among the first to recognize the importance of digital signal processing not only in room acoustics but also in other areas and to actually employ those methods. He used them to generate artificial reverberation and artificial stereophony and applied them in ultrasonics, speech, and electro-acoustics. Manfred was also an innovator in computer graphics; his application of concepts from mathematics and physics to the creation of art gained him top honors in the 1969 International Computer Art Competition.

Among Manfred’s achievements in speech and hearing acoustics are the invention of the voice-excited vocoder in 1960 and the introduction of linear predictive coding in 1967. LPC remains an important technique for analyzing and synthesizing speech and music signals. He also worked on the early development of the concept of surround sound. His mathematical model of the inner ear has inspired much of the work that followed in auditory research.

His interest in mathematics and especially in number theory motivated Manfred in 1984 to write his treatise Number Theory in Science and Communication, now in its fifth edition. The book differs from other texts on the topic in its intuitive approach and emphasis on the application of number theory to such diverse fields as cryptography, physics, computing, and self-similarity. Similarly, his 1991 book Fractals, Chaos, Power Laws: Minutes from an Infinite Paradise illustrates the far-reaching influence of the concept of self-similarity on science, music, and the visual arts. Both books are marvellous examples of how to present difficult subjects with clarity and humor. His third book, Computer Speech: Recognition, Compression, Synthesis, first published in 1999, connects speech recognition and synthesis to monaural and binaural hearing and to modern signal analysis. In addition to those works, Manfred published more than 150 papers and was awarded 45 US patents.

Manfred was a founding member of the Institut de Recherche et Coordination Acoustique/Musique in Paris. His scientific achievements earned him such honors as the Rayleigh Medal from the British Institute of Acoustics in 1987, the gold medal of the Acoustical Society of America in 1991, the Helmholtz Medal of the German Acoustical Society in 1995, and the Technology Prize of the Eduard Rhein Foundation in 2004.

Everyone who met Manfred experienced his kindness, humor, cheerfulness, and ease of communication. His death is a profound loss to the art of combining mathematics, science, and engineering to create outstanding innovations. His many colleagues, students, and friends all over the world deeply miss him.

Manfred Robert Schroeder

Manfred Robert Schroeder

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