My Affairs with Feedback

Words by Alvin Lucier
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Alvin Lucier. Photos by ZV Vasovic

On Thanksgiving Day, 1975, with nothing better to do, I spent the afternoon in the Wesleyan University Electronic Music Studio. I began experimenting with panning the sounds of an electronic birdcall between two loudspeakers. I had recently received the birdcall in the mail from sound artist Doug Kahn, whom I had never met. The birdcall was actually a Christmas tree ornament, a baseball-size silver ball, containing a sound-producing circuit, a miniature amplifier and loudspeaker. It emitted endless repetitions of a downward glissando followed by a series of repeated chirps. Kahn said he thought I might find a way to use it in a musical work.

I had also just acquired a pair of miniature Sennheiser binaural microphones, designed to be positioned on either side of a dummy head or worn in human ears, in order to make realistic recordings. By moving my head back and forth rapidly I was trying to produce short time delays or, since that seemed unlikely, perhaps I would discover some other interesting phenomenon.

At one point, as I was standing in the middle of the room, feedback started to sound. Before I could get to the amplifier and lower the volume control I began hearing phantom images of the birdcall, which seemed to come from inside my head and at the same time to be located in various parts of the room. They were amazing. What I was hearing was heterodyning, a term in radio technology describing beat frequencies produced between two radio frequencies, of which one is usually a received signal-carrying current and the other that of an uninterrupted current introduced into the apparatus. In this case the phenomenon was produced by the interaction between the continuous strands of feedback and the sounds of the birdcall, both within the audio range.

Often the resultant phantom shapes were simply lower transpositions of the original. At other times they were mirror images. If two or more strands of feedback sounded at once, double images might sound simultaneously.

It is difficult to pinpoint the frequencies of the birdcall exactly — the call is noisy — but careful listening puts the start of the swoop at approximately 880 cycles per second (cps), the repeated chirps at 660. The feedback frequencies that produce the most vivid phantoms are in the range of 1750 to 3000 cps. The phantoms themselves sound in the lower mid-range, from approximately 250 to 700. I had originally thought that the images were simply resultant or difference tones. If the feedback sounded above the birdcall, as the birdcall swooped downward, the distance between it and the feedback grew smaller; the resultant tones were lower. If the feedback occurred above, the resultant tones slid upward, as the distance between the two sounds increased. But because of the disparity between the frequency range of the feedback and that of the birdcall, the phantoms must be some form of harmonically related beat frequencies caused by the interaction of a fixed frequency signal (feedback strand) and a search tone (birdcall). Whatever these phenomena might be called, including resultant tones, heterodyne components or inter-aural harmonics occurring only in the brain of the listener, the results are spectacular. Listeners can hear them vividly. The piece is called Bird and Person Dyning.

In numerous performances over the years I have developed a simple set-up consisting of the birdcall mounted on a mike stand and positioned in the front middle of the space flanked by two stereo loudspeakers. The birdcall sounds by itself; it is not mixed into the sound system. The binaural mikes are worn in the performer’s ears, routed by long cables through a mixer with compressor-limiters and amplifiers to the two speakers. Before the performance the performer, with the help of the a sound technician, searches the space for room resonances whose sonic manifestations as feedback, cause heterodyning. During the search process the sound technician uses equalization to help bring out resonances in this frequency range.

The performance simply consists of the performer moving slowly around the space searching for phantoms. When I perform the work I usually move through the audience, toward the birdcall and speakers, stopping briefly when I hear heterodyning. I tip my head from left to right, to fine tune the results and move them to various points in space. The spatial relationships between the binaural microphones and the loudspeakers determine the geographical locations of the phantom birdcalls. I relish the theatricality of the situation. Sometimes the results are vivid — transpositions and their mirror inversions occur. At other times, however, the room just produces a few unwanted resonances. The performer accepts the task of finding the appropriate strands of feedback that create phantom images of the birdcall. The performance is not an improvisation.

It wasn’t until 1994 that I used feedback again for musical purposes. I was asked by Wesleyan University to present a festival of my work. I decided to make as many new pieces as I could rather than resurrect old works to form a retrospective. I made 16 new pieces in one year, most of them prose scores, others simply were verbal instructions. One was a work for Javanese gamelan instruments. For many years I had hesitated to use non-Western instruments in my music. There had been too many such works that seemed to me to smack of chinoiserie. Then too, I didn’t want to intrude on the Wesleyan gamelan master musicians’ time and energy. They had enough to do to maintain a coherent program in traditional Javanese music and dance. But more important, I didn’t want to exploit someone else’s music.

However for several years I had a specific idea about exploring the acoustic properties of certain gamelan instruments. I felt comfortable in doing so rather than referring to the actual music or some hybrid form of Western and Javanese styles. I thought of the bonangs, bronze bowl-like gongs of various sizes, as small environments, the resonant frequencies of which could be revealed. By inserting microphones into the cavities of these instruments and bringing the amplifier gain up to the level of feedback the resonant frequencies would sound. The resulting pitches are variable and unstable and bear no relationship to the struck pitches of the instruments themselves. Often the feedback changes pitch without warning. More often it depends on how deep into the opening the microphone is inserted. Sometimes two pitches sound simultaneously or oscillate in a kind of trill.

Before the performance four performers choose any number of bonangs at random. During the performance they lift them over the microphones mounted on boom stands. As the bonangs sound three gendèr (metallophone) players search for the feedback pitches by tapping series of tones, searching for any one of the feedback frequencies. Since it is statistically improbable for any gendèr and bonang pitch to match, audible beats happen at speeds depending on the distances between the pitches. The farther apart, the faster the beating. And since the pitches of the gendèrs are fixed and can’t be bent, no unisons are possible. To offset that limitation the players slow down and speed up their tapping, arriving at temporal ‘unisons’ with their feedback pitches. The speed of their tapping comes into synch with the speed of the audible beating between the pitch of the feedback and that of the gendèr. This slowing down and speeding up is an indirect reference to Irama, a Javanese musical structure in which certain instruments slow down while others speed up, gradually doubling and halving the tempo simultaneously. The score of Music for Gamelan Instruments, Microphones, Amplifiers and Loudspeakers consists of a set of instructions as well as number systems for the players to follow, allowing for many possibilities in pairing the gendèrs with the bonangs.

In 1997 I composed Small Waves, a 56-minute work for string quartet, trombone and piano with six partially filled water containers. The work was commissioned by the city of Zug, Switzerland, and was first performed there by Hildegard Kleeb (piano), Roland Dahinden (trombone), and the Arditti String Quartet. In this work microphones are inserted into the mouths of small glass jars and vases. When the volume levels of the amplifiers are raised to feedback level the resonant frequencies of the containers are sounded. Throughout the performance the musicians play long tones in upward and downward scanning patterns, creating audible beating which slows down and speeds up as the tones approach and pass the resonant frequencies. From time to time water pourers empty water from one container into another, lowering the pitch of the former, raising the pitch of the latter.

There are six microphones, one for each vessel. The size and characteristics of the microphone and its displacement of air in the container were crucial to the pitch it produced. By pairing each vessel with its own microphone I could ensure that the feedback frequencies were similar each time I set the piece up. It was important, too, that the mikes be lowered into the vessels to the same depth each time. Even with these precautions, the system was so fragile that often I couldn’t replicate the exact same pitches. The players’ scanning patterns often cross the resonance tones, however flat or sharp they might be. Even when unisons are supposed to be reached, their out-of-tuneness is not bothersome. You cannot expect found objects to match exactly the pitches of our tempered scale. Anyway, the rhythms of the beating patterns are more important than accurate tuning.

In a recent recording of Small Waves sound engineer Tom Hamilton asked me why I didn’t simply use sine wave oscillators instead of hard-to-control, unstable feedback. I wasn’t sure why at the time. Then we measured (tuned) the frequency of the feedback from several vessels and discovered wide deviations in pitch and loudness within each vessel. The variations were in real time. The feedback resembled a living organism.

In that same year I presented a sound installation at the Donaueschingen Music Days in Germany, using a similar set-up. In Empty Vessels, eight large melon jars and vases were mounted in a row on a slightly raised stage one side of the room. Microphones on boom stands were inserted into the mouths of the vessels and routed through compressor-limiters and amplifiers to loudspeakers, one for each vessel, hidden behind a curtain on the other side of the room. As visitors entered the space — a school cafeteria, the walls of which had been hung with black drapery — the movement of their bodies disturbed the feedback strands causing ripples of sound, as if in a pool of water. Not only did horizontal movement across the strands cause discernible effects but perpendicular movement as well. People moving toward the vessels caused variations in pitch and dynamics. Every once in a while a vessel would actually stop sounding.

For a few hours each day I would relieve the technician guarding the sound equipment hidden in the balcony. Without looking I knew immediately when a visitor had entered the space by hearing ripples of sound, sometimes very slight changes in equilibrium. It was gratifying to me to see visitors of all ages and types interact with the system. Most of them immediately understood what was happening. The townspeople of Donaueschingen, many of whom do not as a rule attend the scheduled concerts, were regular visitors to Empty Vessels, as well as the several other sound installations mounted in various venues throughout the city.