Diehard Furtwängler partisans hardly need to know more. But why should anyone else spend over £200 on surviving, already widely available excerpts from 21 broadcast concerts in variably overloaded mono sound?

Because, for one thing, these are the recordings that have come, more than any other, to define this conductor’s identity, and his legacy. As someone never fully at ease working under studio conditions, Furtwängler came to make recordings quite late in his career. In 1926 he was 41 years old, with a professional career of more than two decades’ standing behind him, when he conducted the Berlin Philharmonic in Beethoven’s Fifth (reviewed in March 1927, without once mentioning the conductor by name). Emphatic and rhythmically straightforward, this first of 13 extant accounts neither generates the electricity of earlier recordings by Arthur Nikisch and Landon Ronald, nor yet adequately represents how he made the symphony go when unconfined by conducting it in four-minute chunks. With its much wider dynamic range, the 1937 remake issued by HMV (and faithfully transferred in 1996 by Lowell Cross for Music & Arts) more fully conveys the peculiarly dense BPO sonority and the conductor’s instrumental voicing.

But it’s only with the live broadcast from a Berlin Radio studio in September 1939 that we hear Furtwängler uncaged, if you like: less precise in attack than the NBC recording conducted by Toscanini two months later, but in which the Andante con moto is moulded into a series of waves each more powerful than the last, at once over-riding the underlying march rhythm and yet rooting it in the same metrical scheme as the following Scherzo. Here are the qualities of ‘Urlinie’ (underlying melody) and ‘Fernhören’ (literally, hearing from a distance) that Furtwängler learnt from the theories of Friedrich Schenker and the realisation of which in turn prompted Schenker (and others) to set the conductor apart from his peers as a supreme recreative artist.

The 1939 Fifth was recorded on eight single-sided shellac discs, of which the seventh was lost. The transfer on Tahra fills in the missing side with material from 1937, whereas the team of engineers working for the Berlin Philharmonic on the new box has opted to give us what’s left of the performance, no more, no less.

By then Germany was at war, and the degree to which circumstances influence both performance and each listener’s perception of it is a matter of pure conjecture. The 1937 recording in particular establishes a blueprint for Furtwängler’s vision of the symphony that undergoes no radical transformation in any of the 11 subsequent performances left to us.

And yet: shortly before his retirement in 2014, the late Michael Gielen conducted Mahler’s Sixth Symphony at the Salzburg Festival, with the Baden-Baden radio orchestra that had lately been served with a termination notice. He remarked at the time that ‘Crisis also stimulates. One struggles to sustain what one has created.’ It is this sense of struggle – a word that recurs time and again in Furtwängler’s own writing – which surely lends many of his wartime performances their unnerving intensity.

Presentation and marketing also play their parts in perception, and it would be idle to pretend otherwise. Editorial and design between them paint the most sober yet vivid portrait of Berlin at war, and the orchestra too, from beautifully printed imagery of the bombed-out Philharmonie to concert posters, letters, photographs of musicians and broadcast engineers at work, and reproductions of the tape cases which illustrate the tortuous tale of where these recordings came from.

As meticulously outlined by the booklet essays, the first two concerts were preserved on shellac discs, of which original copies have been sourced in Germany and newly remastered. The remaining 19 concerts, or portions of them, were carefully mixed for broadcast by a team of Reichsrundfunk engineers including Friedrich Schnapp, whose recorded recollections – at least most of them – conclude the set: the French Furtwängler Society (SWF) has previously issued a longer version of the interview.

After the war, many of the original tapes ended up in the care of Moscow Radio. This is how some of them were first released in Europe, as more or less decently transferred Melodiya LPs. The generous baritone of Tibor de Machula came over loud and clear as the soloist in Schumann’s Cello Concerto, but the grooves bit and spat at the climaxes of Bruckner’s Fifth from the same concert. Around the same time, DG released LPs of a few tapes left behind in Germany, such as Beethoven’s Fourth Piano Concerto with Conrad Hansen, but the results were, if anything, even dimmer. With the advent of glasnost the Moscow tapes began to trickle back to Berlin, though some of them arrived as copies.

The difference between copy and original (scrupulously outlined by the tracklisting) is laid bare by perhaps the most renowned single performance in the box, of Beethoven’s Ninth from March 1942. This has been transferred from original tapes except for the Scherzo – from a copy – which duly sounds as though it was recorded in a different and more distant acoustic. In an ever more crowded market, the SWF transfer was until recently regarded as the best yet, but there is a quite startling roundness and richness to the new remastering that handles even the apocalyptic climax of the first movement (where Furtwängler always used two timpanists). Comparable to Andrew Rose’s work on Pristine Classical, there is the uncanny suggestion – illusion would be too strong a word – of a soundstage with a definite centre, a kind of ‘wide mono’, without pulling artefacts into distinct channels in the manner of the ‘fake stereo’ of the 1960s. The level of intervention here isn’t made clear, or not as clear as the ‘Callas Remastered’ transfers undertaken by Abbey Road Studios for Warner Classics in 2014, but it isn’t as radical as some Pristine releases.

The audio restoration does wonders for the piano concertos in particular, filling out piano tone and sharpening up high and low registers. The transfers of Hansen’s Beethoven and Adrian Aeschbacher’s Brahms B flat Concerto are as good as new performances, by no means shallow compared to Edwin Fischer’s performances (of the same Brahms and Furtwängler’s own, prolix Symphonic Concerto). Only Walter Gieseking’s Schumann still disappoints, with the conductor’s contribution equally (and uncharacteristically) disengaged as his soloist’s. Meanwhile the coughing throughout Hansen’s sublime prolongation of the Fourth Concerto slow movement’s coda is still present, and so is an odd clicking at 1'40"-1'50" of the Schumann finale.

From the same concert as the Schumann, however, comes a Beethoven Seventh that burns with the kind of fury so impotently expressed by Furtwängler in his diaries. The speed of the finale is pretty much identical to when the orchestra played it last summer under their new chief conductor, Kirill Petrenko, but Dionysiac fury is played out through tragedy, as it is in Schubert’s Great C major. In Strauss’s Don Juan and the Tristan Prelude and Liebestod, Eros is put to the service of the same muse. Even the openers to Der Freischütz and Die Meistersinger contrive, without perversion, to rage with joy. In the unequivocal tragedies of Beethoven’s Coriolan, the Fourth Symphony of Brahms and the Ninth of Bruckner every phrase sounds as if scored into the manuscript paper with the blackest Indian ink.

The tracklisting also lays out, in ghostly, grey type, what we have lost from several of the concerts. Much of it is new music, composed by Philipp Jarnach, Paul Höffer and Gerhard Frommel, of the kind Furtwängler tended to promote as an act of resistance to the new orthodoxies of Schoenberg and Stravinsky. As the examples of Ernst Pepping’s Second Symphony and Heinz Schubert’s Hymnisches Konzert demonstrate at some length, it was a style condemned to obscurity by its own anachronistic worthiness, and Furtwängler entertained similar (justified) fears about his own music.

However, what survives of these concerts comes down more to the hand of fate than the capricious aesthetics of any radio producer. A Mozart Symphony No 40 is missing, a Brahms Second, more Fifths and Sevenths of Beethoven. More grievous is the loss of the first movement to a Bruckner Sixth fired with nervous, Schubertian energy even in the funeral march of its slow movement. One notable act of restoration comes with the penultimate concert, and a now complete (not completed!) Unfinished Symphony.

But inevitably, before the interview with Schnapp, the musical climax of the box arrives with the finale of Brahms’s First Symphony, recorded in the cavernous Admiralspalast on January 23, 1945, before Furtwängler fled to Switzerland. Were I asked for a single recording to show ‘why conducting matters’, I would choose this Brahms performance, a bloody torso as it is. The canard that Furtwängler could not secure an exact, unanimous attack is rendered more baseless than ever by the new remastering.

Another canard is dispatched by archival material that shows how concerned the conductor was with the fidelity of these live recordings, and by their contribution to his legacy. ‘It never comes out on the radio the same way I conduct it,’ he complained to the long-suffering Schnapp, who concludes that ‘he never agreed with the cultural policy of the Nazis … He was human – what can I say?’ Were not idea and execution so perfectly aligned, so often, in the performances so reverently enhanced by this box, there would be no need for anyone to take sides over Furtwängler’s own degree of political alignment. History wouldn’t care. He’d be another Nazi stooge, another useful idiot, or not. But these are the concerts that, so they said later, made life worth living for many Berliners. They matter.