Gabriel Weinreich and Directional Tone Color

“When I say I study violin acoustics,” says Gabriel Weinreich, Professor Emeritus at the University of Michigan in Ann Arbor and preeminent figure in the world of musical acoustics, “people ask me if I’ve found the ‘Secret of Stradivari.’ Well, I suppose it was the instrument’s mystique that attracted me in the first place. Why is it so difficult to make very good violins? I started looking at such questions in the mid ‘70’s, and naively thought that all you needed was a competent person with a year or two to do some serious research.” He leans back in his armchair and laughs. “Twenty five years have gone by and I still don’t know the Secret of Stradivari – which is not to say I haven’t learned anything! It’s just that the question has changed. The question ‘what makes a good violin’ has broadened into many separate questions, each requiring its own answer.”

The question of why is it so hard to reproduce the sound of the violin has eluded recording engineers ever since Pablo Sarasate stood in front of a rotating wax cylinder more than a century ago. Though it is now possible to make “high fidelity” recordings of many musical instruments, even with the best equipment the sound of a solo violin seems to lose something important in the journey between microphone and loudspeaker. Just what is lost has been made brilliantly clear by Weinreich’s recent theory of Directional Tone Color (DTC for short). “The human voice and most orchestral instruments,” he explains, “send out sound without much regard to direction through most of their range. But stringed instruments (as well as the pipe organ) are highly directional. From note to note, the harmonics are radiated in ever shifting directions. Even the slight changes in pitch created by vibrato can cause these harmonics to change direction radically. Imagine beacons of sound, like the quills of a porcupine, undulating continually. The ear is not clever enough to figure out exactly what is happening, but it is plenty clever enough to sense that something is happening! In fact DTC may be one reason vibrato is used so universally by violinists – as compared to wind players, whose instruments generally lack directional tone color.”

It may also explain, says Weinreich, the characteristic “flashing brilliance” of virtuoso playing, and solo virtuoso’s uncanny ability to be heard above an orchestra – even with whole string sections playing at roughly the same dynamic level. Because the details of DTC vary randomly from violin to violin (or viola to viola), when a dozen are playing in unison the effect is almost completely averaged out. The somewhat mysterious quality of ‘projection’ may be partly the ear’s tendency to notice a tone which has DTC against a background of tones which do not. As loudspeakers are designed not to have directional characteristics, it is no surprise that they fail to convince the ear it is in the presence of a real violin.

Known to friends and colleagues as Gabi, Weinreich is one of those joyfully articulate people who speak in publishable sentences. He can carry an idea, in the face of digression and interruption, with the agility of a star football player carrying a ball down the field. Weinreich was born in Vilna, now capitol of Lithuania, then a part of Poland. After the Germans invasion of 1939, he and his mother escaped by train across Siberia, eventually rejoining his father and brother in New York City. His father was one of the founders and Director of the YIVO (Yiddish Institute) and a linguistic scholar of international repute.

Music was always part of Gabriel Weinreich’s life. He took piano lessons briefly as a child, and many years later took up the cello. As a teenager in New York he studied music theory with an elderly gentleman from St. Petersburg – a onetime student of Rimsky Korsakov. But Weinreich knew from an early age that he would be a scientist. Leaving Vilna under the most difficult conditions, he persuaded his mother to let him take two books by Jules Verne. He eventually enrolled in City College, New York, in Chemical Engineering. But a meeting with an old school friend changed his direction. “Chemical engineering?” his friend exclaimed. “There is only one place for great minds like ours – physics! Physics is the only place for genius!” Weinreich promptly switched fields; his friend did an about face and tried to become a screenwriter.

Weinreich likes to say he came to musical acoustics on a dare, the challenge being to get funding for a subject that was not yet part of university programs in the United States. He soon became the first in the field to get what he calls “normal college funding.” As it happened, musical acoustics inadvertently gained the support of the United States government thanks to the Cold War. The Pentagon was interested in tracking Soviet submarines using sonar, and so wanted to learn everything they could about sound. Weinreich’s initial work was with the piano. His results made the cover of Scientific American and his reputation was established.

In a sense DTC has brought Weinreich’s career full circle. He began his work with violins by looking at their directional properties. The DTC concept developed in his mind for many years, but only after retiring from teaching did he find the time to do the necessary research. He also invented a speaker capable of restoring DTC to recorded violin sound. It works by creating hologram-like interference patterns at the ends of four differing lengths of pipe. The differently vibrating areas of a violin body create the effect in a somewhat similar fashion.

Weinreich takes me down to his brightly-lit laboratory. The room is dominated by a large, well-insulated interior room whose walls, floors, and ceiling are completely covered with geometrical arrays of white and gray foam pyramids. It might be a high fashion hair salon – except for the violin suspended in a metal frame, a phonograph cartridge resting on its bridge, a tangle of wires leading to a computer outside. In fact the room is an anechoic chamber (literally, a room without echoes), something as useful to an acoustician as a couch is to a psychoanalyst. The lab is otherwise populated with racks of audio gear and electronic devices. Cartoons are taped to the wall near the door. High shelves are filled with dismembered equipment. An Einstein calendar offers a thought for the month.

Weinreich points out the prototype DTC speaker, a plywood box sitting on the floor, four unequal lengths of gray plastic pipe extending from its top surface. To demonstrate he asks his assistant, Colin Holmes, to remove the top from the device. Underneath is an ordinary speaker. Weinreich drops a CD into a player and Henryk Szerynk begins to play unaccompanied Bach. The sound seems to emerge quite normally from the speaker, as it would on any good mono recording. But when the top bearing the pipes is replaced, something remarkable happens. The sound of the violin fills space in completely different way. It is as though a violin of indefinite size is dancing in the air above the speaker. The sound, like that of a live violin, is enveloping rather than direct. When Weinreich puts on a recording of a pipe organ, the effect is even more impressive.

Gabriel Weinreich

No less qualified a listener than Pierre Boulez once observed that loudspeakers have the property of “anonymizing” the sound of musical instruments, of making them all sound the same. This is damning criticism in view of the claims to “high fidelity” made by manufacturers and sellers of audio equipment. The term “High Fidelity” rouses a bemused skepticism in Weinreich. “There is a story of a salesmen demonstrating Edison’s phonograph, switching between a live singer and a recording of her voice. Apparently the audience could not tell when the singer stopped and the phonograph started. Now if you’ve ever heard one of those phonographs, this seems an extraordinary claim. But we have to remember that in those days people had never heard a recording before. And so the illusion may have been convincing – at least for a while.”

There is a similar story about early motion pictures. People were said to have run from the theater in panic when an actor on screen drew a gun and pointed it at the audience. While it is possible to fool the eye or the ear for a time, our senses seem very good at sorting out such illusions. Of course engineers then scratch their heads and find ways to create more convincing illusions. “There are so many people willing to spend money on audio equipment that progress has been very rapid. In a sense the technology has far outstripped any understanding by its creators of what the technology is supposed to do. High fidelity to what? Do you want it to be as though the Berlin Philharmonic is actually in your sitting room? Of course most popular music today is created electronically, and so it can be heard only through loudspeakers. The question of fidelity becomes trivial. But if you want to reproduce perfectly the acoustical experience of being at a string quartet concert, you’re out of luck. But the DTC Speaker can add another dimension to the illusion.”

And how does the DTC Speaker fit in with the concept of Stereo? “In a way,” says Weinreich, “stereo stumbled on DTC inadvertently. Though primarily intended to give a spacial sense to music, interference between the two speakers creates a more complex sound field, one which to some extent emulates what a violin does.” One particularly exciting use for the DTC speaker is, to my mind, for enhancing the tone of electric violins and electronic synthesizers. Playing a solid body violin through Weinreich’s prototype speaker, I was astonished by the degree to which the violin’s characteristically undistinguished sound became suddenly responsive to vibrato. The sound took on something of the beauty I usually associate with old wood, worn varnish, and Italian labels. As a violinmaker, I have spent years trying to coax this kind of beauty from my own instruments. Now here it was, emerging in full flower from the open ends of four plastic sewer pipes.

Gabriel Weinreich and Joseph Curtin

Weinreich and Curtin with DTC speaker at Weinreich’s University of Michigan lab

Although the device has been patented by the University of Michigan, it has yet to be developed commercially. Is Weinreich interested in pursuing its development? “We scientists,” he says in a gently philosophical tone, “tend to lose interest in doing something as soon as we know how to do it. Once we know how to do something, we tend to start looking for something we don’t know how to do.” Much like good artists, I think. But in an industry intent on selling any number of musically irrelevant effects, I can only hope that manufacturers will take an interest in what Gabriel Weinreich knows how to do.