Piano accompanist with a luminous tone and a scrupulous regard for phrasing
Perhaps destined by his parents' choice of forenames to pursue a musical career, Martin Johannes Sebastian Isepp, who has died aged 81, established himself in Britain after the second world war as the accompanist of choice to many distinguished singers, including Janet Baker, Elisabeth Söderström, Elisabeth Schwarzkopf, Jessye Norman, Hugues Cuénod and John Shirley-Quirk. He was highly valued too as a coach and mentor to generations of singers at Glyndebourne, where he was head of the music staff from 1978 to 1993.
His father, Sebastian, was an accomplished artist and art restorer; his Jewish mother, Helene, was a singing teacher whose pupils included Baker, Ilse Wolf and Heather Harper. In 1938 the family fled from Martin's birthplace of Vienna to England. After attending school in Bognor Regis and Shrewsbury, he followed his parents to Oxford, where his father had been offered a job at the Ashmolean Museum. In Oxford, Leonie Gombrich, mother of the art historian Ernst Gombrich, gave Isepp private piano lessons, and his formal education was continued at Lincoln College, Oxford, and the Royal College of Music.
He began his career with the English Opera Group, taking the piano part in the first performance of Benjamin Britten's Turn of the Screw. In 1957 he joined the music staff of Glyndebourne Festival Opera, where he began to make his indispensable contribution – none the less so for being behind the scenes – to British operatic life.
Serving simultaneously at Glyndebourne and as head of music studies at the National Opera Studio in London (1978-95), he coached countless aspiring singers and continued to visit Glyndebourne as chief guest coach for many years after his retirement. His other notable posts included head of opera training at the Juilliard School of Music, New York (1973-77), and head of the academy of singing at the Banff Centre in Alberta, Canada (1981-93).
A gentle, unassuming man, Isepp nevertheless had a reputation as an exacting, rigorous coach, concerned for the precise shaping of every phrase. Not for him, though, the brusque manner of a martinet when a student failed to rise to the occasion: rather a disappointed sigh and an exhortation to do better. Of Mozart's operas he had an intimate knowledge, frequently abandoning scores while coaching.
That scrupulous regard for phrasing, combined with a luminous tone, also made him an inspirational accompanist for some of the leading artists of his time. Among his various partnerships, that with Baker in glorious voice, perpetuated on a pair of recordings for Saga – an anthology of English song (1962) and a disc of Schubert, Schumann and Brahms lieder (1966) – will be most highly treasured by record collectors and lovers of art song. Isepp's ability to conjure a rapt atmosphere, to build and sustain a climax that fully supports the singer, and his eloquent postludes all combined to make him one of the most sentient of accompanists.
Isepp was also a more than competent conductor, as he demonstrated both with Glyndebourne Touring Opera and at the New York Met, where he stood in, during his tenure as assistant conductor for the company, for an indisposed James Levine in a run of performances of Così Fan Tutte. As a continuo player, too, he was responsible for a number of imaginative reconstructions of baroque operas.
He is survived by his wife, Rose, whom he married in 1966, and by two of their three sons.
• Martin Johannes Sebastian Isepp, piano accompanist, born 30 September 1930; died 25 December 2011
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