The Swedish conductor Arnold Östman (born in Malmö, 1939), who died on 15 August at the age of 83, made commercial sound recordings of just six classical operas – but the four most important of these transformed the way we experience and think about Mozart’s greatest dramatic masterpieces.

After studying Art History, the harpsichordist pursued musical studies in Paris and Stockholm. In 1969 he began a 13-year association with the opera academy at Vadstena, a summer festival held near Lake Vättern in southern Sweden, where he encouraged experiments with Baroque operas by Purcell, Monteverdi, Provenzale and Stradella throughout the 1970s.

In 1979 he conducted for the first time at Drottningholm Court Theatre – an extraordinarily intact, beautiful and well-preserved 18th-century opera house built in 1766 at the summer palace of the Swedish Royal Family by Lake Mälaren about 12 miles west of Stockholm, and with its stage machinery, sliding scenery flats and special effects (wind and thunder contraptions) in perfect working order. On the back of this successful production of Don Giovanni (using anachronistic Baroque instruments that he later acknowledged as ‘harsh, brutal, banging … with heavy, countrified colours’ that were not right for Mozart), Östman was appointed Artistic Director, and within two years he had switched to the innovative use of Classical period instruments for an orchestra featuring a smattering of British leading exponents including concertmaster Simon Standage alongside young Swedish musicians eager to learn how to master historical performance practice on old instruments or suitable copies.

Östman served as Artistic Director and conductor at Drottningholm until 1993, by which time they had made revelatory (and sometimes controversially fleet-footed) recordings of Mozart’s Da Ponte trilogy and Die Zauberflöte for Decca’s early music imprint L’Oiseau-Lyre. Moreover, Swedish TV broadcast Drottningholm’s staged productions of the same operas with different, less starry but capable casts, and also playful yet sincere semi-historical productions of La clemenza di Tito (1987), La finta giardniera (1988), Die Entführung aus dem Serail (1990) and Idomeneo (1991) – many of them in collaboration with stage producer Göran Järvefelt. Östman also pioneered operas by Gluck, Kraus and Cimarosa. Meanwhile, at the Baroque theatre in Schwetzingen (near Stuttgart), he conducted productions by Michael Hampe of Handel and Salieri.

In later years Östman returned to Drottningholm on several occasions, most notably an ambitious Gluck season in 1998 that yielded the first (and still the only) period-instrument recording of the composer’s original Italian-language version of Alceste (Vienna, 1767), issued by Naxos.

Soon afterwards, he played a key part in establishing annual festivals of Baroque and Classical opera productions at the smaller rococo theatre Confidencen (1753) at Ulriksdaal Palace (also near Stockholm), including works by Monteverdi, Stradella, Gluck, and, of course, Mozart. In 2010 he received the medal of the King of Sweden for outstanding contributions to Swedish musical culture.

The conductor’s artistic principles were best summed up in his manifesto published in the booklet for his radical yet intimate recording of Così fan tutte (1984), not only the opera’s first truly complete recording, but also the first commercial account of any Mozart stage works to be played on period instruments; indeed, Östman described Drottningholm’s theatre as a period instrument in its own right: ‘The dialogue with the theatre itself is often a surprising and exciting experience, revealing unknown problems and possibilities. The acoustic gives a new proportion to all tempi, nuances and expression, and the singer has to react with a flexible approach in which the smallest nuances can create the most human portraits. The instrumentalists, too, must play like chamber musicians in order to produce a legible and balanced sound. … Our work develops from this subtle, living sound. Such conditions provide a good answer to the problem of “authenticity”. We don’t need to create a style, we simply react to what exists around us. We know how easily stylistic discoveries can be transformed into clichés, so that in the end we are back again with a performance tradition which has nothing to do with artistic freedom. Instead, the experimental and improvisatory approach which Drottningholm inspires stimulates us to give … a performance of originality, exciting improvisation, strength and grace.’

Stanley Sadie acknowledged that Östman’s Mozart series ‘set new standards in period-style performance of these works and did much to enhance general awareness of the advantages of light instrumental textures, lively tempos, stylish ornamentation and observation of the obligatory appoggiaturas.’

All three of the Da Ponte operas featured bonus tracks of discarded arias or music composed for Mozart’s own later revivals: the more elaborate arias for Susanna in the 1789 revival of Figaro (among other variants), all of the material Mozart used for substitutions and additions in the Vienna version of Don Giovanni, and Guglielmo’s discarded aria ‘Rivolgete a lui’ (which Mozart replaced with ‘Non siate ritrosi’).

Alan Blyth’s rapturous verdict that Östman’s Die Zauberflöte (1993) ‘offers the nearest to perfection one can expect in an imperfect world’ still rings true to some of us.

Upon witnessing full rehearsals that led to the recording of Le nozze di Figaro (1988), Stephen Pettitt pointed out that the music director preferred ‘that people remember his performances as Mozart’s Mozart rather than Östman’s, which, in an age that sees heroes in conductors who distort for the sake of promoting the personality cult, is surely only right.’

Östman himself told Gramophone on the release of Don Giovanni (1990) that ‘It’s so important to use classical instruments. We make mistakes with them, but we keep trying because it is really important complementary information, which has a scientific value. Yet we don’t use it as scientists, we use it for artistic freedom. The more information you have, the more freedom you have.’