Of the many prestigious music festivals in Europe, Salzburg remains the non plus ultra. With an annual piggy-bank of €60 million, it is no wonder. The pantheon of premier orchestras and conductors on the programme reads like a musical Debretts: Barenboim, Muti, Marriner, Chailly, Rattle, Dudamel, Nézet-Séguin; the Vienna and Berlin Philharmonics, Amsterdam Concertgebouw and Cleveland Orchestra all illuminated the 2016 Salzburg galaxy. In such stellar company any new ensemble, especially one without appellation, will be subject to especially severe scrutiny.

Such was the case with the chamber music concert convivially described as “Anna Prohaska, Veronika Eberle & Friends”. Whilst soprano Anna Prohaska is undoubtedly a rising star in the lyric firmament and Veronika Eberle an acclaimed violinist, this pick-up ensemble of amigos had little other than the Schwetzingen festival in May on which to base its musical credentials. A rather esoteric progamme didn’t make things any easier. Schubert and Pergolesi’s settings of Salve Regina, the quick and quirky “Schmerz immer Blick nach oben” by Webern and the quasi-symphonic Octet in F major, again by Schubert, made for an extremely original evening in the Mozarteum Grosser Saal.

From the first bars of Schubert’s crypto-religious concert aria for soprano and strings, it was clear that this was definitely no B-Grade divertissement. A wonderfully warm string colour and immaculate phrasing gave immediate elegance and assurance to the instrumental accompaniment. Viennese soprano Anna Prohaska grew up in the house in which Johann Strauss wrote Die Fledermaus, and whilst the voice has a limpid, crystalline quality, it is definitely a lot more than froth and bubbles.

Her acknowledged role model was Hilde Gueden and there are certainly a lot of similarities in purity of tone and effortless legato. Having just sung Susanna in Sven-Eric Bechtolf’s new production of Le nozze di Figaro, it was interesting to observe how the attractive young soprano was able to move from a somewhat frivolous stage characterisation to a thoughtful, emotionally engaged recitalist. There was consistently excellent breath control over the long phrases and the gentle melodic line was embellished with delicate ornamentation and trilling such as filii Evae and Nobis Jesum. Latin scholars or old-school lawyers would have appreciated Prohaska’s immaculate diction.

There were fireworks aplenty in Webern’s curious, dissonant and almost unbearably bleak Schmerz immer concert aria. The Haiku-esque text of a mere 13 words afforded the opportunity for some real vocal gymnastics with enormous leaps reminiscent of Cathy Berberian. This validated the verdict that Prohaska has not only an immaculate vibrato-less clarity to her voice but formidable technical skills as well.

In an age when the Grim Reaper seemed particularly eager to dispatch both prodigies and profligates, Giovanni Battista Pergolesi was only 26 when he joined the angeli in caelis. Perhaps prescient of his impending demise, his setting of the Salve Regina was written in the sombre key of C minor and is much more angst ridden than Schubert’s later adaptation. In this difficult aria, Prohaska again employed her impressive breath control to the utmost and there was some fine word colouring in In hoc lacrimarum valle. The agitato Ad te clamamus middle section displayed a dramatic intensity rare in refined recitals.

The second half of the programme brought accomplished french horn player Radovan Vlatković to the coterie in Schubert’s lengthy Octet in F major. Lasting slightly over an hour and in six movements, this work is symphonic in scope. Former Berliner Philharmoniker first viola Danusha Waskiewicz gave breadth to the string side which almost seemed in amicable competition with clarinet, bassoon and horn sitting opposite in a kind of male vs. female tussle with double bass player Rick Stotijn and cellist Quirine Viersen providing a determining equilibrium. “Schwammerl”, Schubert’s usual melancholia about his apparent failure as an opera composer, not to mention his debilitating social disease, hardly seems in evidence in this essentially jolly composition, especially in the Ländler-rhythmed fifth movement which skipped along with vigorous syncopation. Veteran clarinettist Pascal Moraguès excelled in the tricky long-phrased Adagio and his thematic exchanges with Marco Postinghel’s chuckling bassoon in the Allegretto trio variations were crisp and pungent. Second violin Heather Cottrell provided more than adequate support for Veronika Eberle’s lead and the string introduction to the slower third movement trio displayed commendable parity of tone. Prohaska has good taste in friends.

At the conclusion of the octet, the soprano rejoined the ensemble and in a short and genial introduction extolled the virtues of Schubert’s neglected operas. By way of affirmation she sang Eberhard Kloke’s arrangement of “Ich schleiche bang und still herum” from the Singspiel Die Verschworenen oder der Häusliche Krieg which again displayed the refulgent cantilena of her voice abetted by beautiful clarinet playing but hardly made one pine for a full production of this recondite opus.