Tonight’s Stockhausen Prom was in equal parts sonic experience and performance.

In an introduction to a performance of Gesang der Jünglinge in 2001, Stockhausen proposed that “if you close your eyes every now and then, you might even see these angels”. In a concert performance this isn’t an empty suggestion; Gesang der Jünglinge is a truly acoustic experience. The work is pre-recorded and played through four speakers set around the performance space, the various sounds “moving” palpably around the audience, sometimes in circular or linear sweeps and at other times through a more pointillistic delivery. As such, to listen through a simple home stereo set-up is misrepresentative. It results in an overlap of channels, thus compromising the scale of perceived movement that is integral to a full appreciation of the drama and development of the composition. Furthermore, the blending of the acoustic and electronic components in the work were noticeably effective as a result of the four channels and the rich acoustic of the hall.

The work itself comprises a recording of a boy soprano (Josef Protschka), electronically generated sine waves and electronic clicks, blended together into sometimes indistinguishable fusions of sound. The boy is recorded singing eleven verses from the Bible’s Book of Daniel, each of which begins with the refrain “Preiset den Herrn” (“Praise ye the Lord”). As a result of Stockhausen’s manipulation of Protschka’s voice (overlapping and rearranging certain words, syllables and phonemes, and dividing them between the four speakers), some verses are rendered unintelligible whilst others are set in relief against the silence – kind of structural landmarks.

As is typical of Stockhausen’s music, timbre and texture are noticeably salient features. The various constituent elements are, for example, sometimes manipulated to sound as if they are rising from underwater and at other times as though they were a few feet from the audience’s ears. At one point, sibilant consonants, for example in the word “Eis” (“ice”), are elongated and beautifully blended with electronically generated chime tree and maraca sounds.

The second and final work of the evening was Welt-Parlament (“World Parliament”), an a cappella scene from Stockhausen’s Mittwoch (“Wednesday”) from his cycle of seven operas entitled Licht (“Light”). In this scene, delegates convene at the top of a skyscraper in order to debate the meaning of the word “love”, performed tonight in a mixture of German, English, and Stockhausen’s own invented languages. In spite of the incomprehensibility of his imaginary tongues, the meanings were often very communicative as a result of the way in which he constructed these languages. At one point, for example, a heated debate appears to take place between two members, conveyed by the overuse of sibilant and palatal consonants and highlighted further by the physical gestures of the singers, including finger-clicking. Overall, Stockhausen’s omission or emphasis of certain consonants and vowels was both expressive and provocative, conveying both the extremes of agitation and agreement or strong, rhythmic metres and indistinct ebbs and flows. Indeed, it is a testament to the composer that he is able to sustain a sense of plot progression purely through vocal noises, physical gesture and abstract musical development.

The performance begins before the singers walked on stage, each holding a clicking metronome to their ear as they proceed to their onstage seats, keeping to their own tempo for approximately the first ten minutes and singing in twelve separate groups. Keeping the singers to their individual tempi, the metronomes also become a textural feature: when the overall dynamics dipped, the cross-rhythms of the metronomes became clear, like charges of static electricity sparking through the vocal texture. This was also the case when hard consonants from the high voices pierced long, droning vowels from the men on the left of the stage.

The choir Ex Cathedra and their director Jeffrey Skidmore (whose discography include a conspicuous amount of contemporary music) performed the scene at the world première of the complete opera in 2012 and it was exciting to hear them tonight. The twelve separate groups were well unified, both with each other and with Skidmore, particularly in the ebbs and flows of the rhythmic triple-time section early on in the scene. The overall blend was also very convincing, particularly the seamless interweaving of the various groups as they assumed different degrees of prominence as the performance progressed. It was tantalising, for example, when layers of sound were gradually stripped away to reveal a rich and gentle sustained note sung by the women. This particular aspect is as much a result of the ensemble as it was of the overall balance controlled from the mixing desk, by Kathinka Pasveer (each singer had an individual microphone).

An unforgettable and thoroughly convincing performance.