Sequitur XIII for extended piano & live electronics (2009) is part of a series of works that Karlheinz Essl composed for various solo instruments. The solo piano in Sequitur XIII is accompanied by live electronics, which record the piano part as it is performed live, alter it, and play it back during the performance according to built-in chance operations that cannot be predicted by the performer. This real-time processing “creates a situation like moving in a house of mirrors where the identities become blurred.”
One noteworthy aspect of the piece is that Karlheinz Essl calls for two different kinds of bows to be used, namely, bows with horsehair or fishing line and the e-bow.
In his introduction to a performance of the piece that we made together, the composer described his intention to avoid the piano’s typical sound characteristics in which tones have sharp attacks and then decay to inaudibility; he wanted instead to generate sustained or swelling tones similar to stringed instruments. Experiments led him to the insight that “one can use an electromagnet to prompt the strings to vibrate and thereby produce sustained tones that sound almost like sine waves.” Essl used an e-bow for this, which he learned about through his own earlier experience as an electric guitarist and applied here to piano strings. Additionally, in this piece, we find the familiar technique of stroking the strings with bow hairs.
Because the hairs sound a bit “raspy” and can easily break, a now-perfected technique is used in which a single strand of thin fishing line is attached to a piano string and stroked with bow rosin, which sounds “almost like a sitar.”
Although it too can produce sustained pitches, the e-bow generates tones that have few overtones, and sound more neutral and artificial when compared with the overtone-rich “drones” (as they are called in the score) produced by the strokes of bow hair and fishing line. The e-bow allows only a small dynamic range, which is influenced by slow pedaling or by silently depressing keys. The bowed drones can be modified to a much greater extent. For example, when gently stroking the upper end of the bow, overtones are predominant before a rich fundamental tone emerges.
The e-bow remains for nearly the entire piece on “middle c,” which is a central tone that links the three foundational overtone series used in the composition. It serves, on the one hand, to focus the sounds and resonances and, on the other hand, it can create islands of reduction and clarification. In contrast, the drones are assigned to specific overtone series and enrich the surrounding material with the resonances triggered by the bow. Because the complex drones always sound together with the more neutral e-bow, there is a unique blending of sound in these passages, which I perceive as a synthesis of the opposite poles of the timbral extremes. The extent to which this can be heard in any performance is, however, determined not least by the live electronics. Aside from sustained tones, the piece also has a lot of percussive sounds and repeated notes, whereby rapid reiteration and noise-trills suggest a convergence of the two antipodes.
Find the score and various realizations of the piece on Karlheinz Essl's website