The fragile, stuttering tones died away, and pulling the instrument away from her lips, the trumpeter looked uncertainly around the group of instrumentalists sat with her on the stage.

“What I loved about that was the way that the music started to breathe when you yourself had to take a breath. Think about how important silence can be when we improvise.”

These are the words of violinist/violist Gunda Gottschalk, who has been at the forefront of improvised music for over two decades, both as a soloist and in a variety of ensembles including the Wuppertaler Improvisations Orchester and the new music quintet Partita Radicale.

Invited to give a series of workshops at the Freiburg Music University as part of its improvisation week Open Your Ears!, Gottschalk was asked to lead a group of students in the creation and performance of The Improvised Piano Concerto as part of the closing concert; “Happy Birthday, John!”, a dedication to John Cage who would have celebrated his 100th birthday this year.

Although his music cannot strictly be described as “improvisatory”, Cage would surely have appreciated Gottschalk’s sentiments. He described music as “simply a way of waking up to the very life we’re living”, and his use of compositional indeterminacy (music structured by a succession of “chance happenings”) strives to give events decided by the composer, the performer, and the unpredictable sounds of our surroundings an equal priority.

The Freiburger Schlagzeug Ensemble opened the evening with a version of Cage’s Music for Carillon (edited for the occasion by percussion Professor Bernhard Wulff), in which graphically notated “clusters” and single tones are realised through a variety of “bell-like sounds”. The effect was beautiful, small peals resonating from all corners of the hall, bound together by an enveloping stillness. Despite their quiet dynamic, the fine playing of the ensemble lent each individual sound a particular gravity, as if one was listening to the clamouring of a city’s churches and cathedrals from on far.

An improvisation for organ, harpsichord and piano followed, in which the performers had taken an extract from Cage’s book Empty Words: Writings ’73–’78 as source material. Choosing to substitute each vowel in the work with an undefined chord, and each consonant with a single note, the trio’s translation of the writer’s abstract words and letters was startlingly clear. An ever-increasing freedom of interpretation resulted in a rapidly thickening texture, in which the opening motifs became consumed in a furious rapid fire exchange of chords between the three instruments.

Johannes Lang made interesting use of the harpsichord’s body and strings, using a bold array of percussive slaps, strums and strikes. Sadly, as the trio began to play simultaneously, the organ and piano became rather dominant and the colour of the harpsichord was rather lost.

György Ligeti’s uncompromising lust for the experimental, for new sounds and new techniques to produce them was evident in his study for solo organ entitled Harmonies, itself inspired by John Cage’s compositions for prepared piano. Seeking to challenge every conceivable aspect of the instrument’s social and musical tradition, any concept of form or line is swallowed up by wheezing, microtonal nightmare shadows; bizarre, eerie and deathly cold.

Assisted by three registrants who pull out the stops to varying degrees and adjust power to the bellows, the organist is required to play clusters with both hands, which metamorphose into a grotesque series of crescendos and diminuendos. The partially opened stops provide the “pale, strange and vitiated” tone colour asked for by the composer, and the varying bellow technique results in a continuous glissando effect in which no specific tones are discernible. It was grippingly performed by Professor Martin Schmeding and his three assistants.

The Improvised Piano Concerto took the form of three movements, each in turn spontaneously conceptualised and directed by a member of the mixed ensemble of nine players. The four soloists played on two different pianos, one having been “prepared”, various objects being placed in amongst the strings in order to alter the sound.

The colours of this instrument provided some of the most interesting moments, Cesar Masano’s subtle use of percussion mallets on the strings summoned a sound reminiscent of Indonesian gongs, and his swirling, whispering length of metal chain laying the foundations for an expressive horn solo in the second movement, delicately formed by clarinettist Hannah Seebauer.

It was fascinating to see how each performer’s contrasting musical profile influenced their contribution, jazz pianist Raphael Lott steeping the first movement in a pulsating, percussive groove and flamboyant percussionist Wencheng Lee directing the final tutti chords with infusive pantomime bravado.

The texture of the outer two movements was generally rather thick, and one wished at times for a greater transparency in which individual instrumentalists could have further explored tonal possibilities, or built more intimate dialogues within the ensemble.

However, a wonderfully inventive nod of the head to Cage’s indeterminate aesthetic, in which exploding soap bubbles were used as a “score”, was typical of the sense of spirit and imagination in which this project was created and performed. Happy Birthday, John!