Bruno Walter is on coruscating form in Beethoven's Egmont Overture at the start of a Salzburg Festival concert with the Vienna Philharmonic, given on August 24th, 1950. After this incendiary start, the main work is Mahler's Symphony No. 4. This is simply lovely. Walter conducts with infinite affection, injecting the first movement with an underlying animation and producing balance of almost Mozartian lucidity, helped by refined, sensitive playing. The second movement unfolds without exaggeration, while the hymn-like theme of the slow movement unfolds with heart-stopping nobility: it's extraordinarily moving here. Irmgard Seefried brings touching simplicity to the sung finale: nothing is arch or self-conscious, and Walter captures just the right mood of enchantment. The sound of the ORF tapes is good for its age, making this a historical release to cherish (Orfeo C818 101B, 1 hour 3 minutes).

Kirsten Flagstad sings Wagner and Strauss in live performances recorded in Berlin on May 9th and 11 th, 1952. Flagstad is in fine voice, and George Sebastian is an imaginative and dramatic conductor whose experience in the opera-house is put to good use here. In the Wesendonck-Lieder Flagstad sounds more youthful than in her later studio recording with Hans Knappertsbusch – her voice has greater richness here, with few if any signs of age. Sebastian's conducting of the Tristan Prelude is excellent and Flagstad is strong in Isolde's narration from Act I, straining only for a couple of high notes. In the closing scene of Act 3 (not just the Liebestod but the Lament preceding it) Flagstad's feeling for line produces singing that is intense, focused and secure.

The second concert opens with three of the Four Last Songs that Flagstad had created in London with Furtwängler a couple of years earlier; in these Berlin performances the sound is far better. She sails over the orchestra in 'Beim Schlafengehen' and 'September' and 'Im Abendrot' are both sung with the same kind of unforced eloquence. Hearing this great operatic voice in these songs puts them in a different light from those of some of her famous successors. After an impressively dramatic extract from Elektra (the monologue beginning 'Orest! Orest! O lass deine Augen') the concert ends with the Immolation scene from Götterdämmerung. This is an overwhelming treat: Flagstad sounds even more involved than in her studio recording with Furtwängler and the Philharmonia made six weeks later, and Sebastian's conducting is sensitive and exciting. The last chord seems to end too abruptly, but the sound is admirably clear and full. This very satisfying Flagstad collection comes with a booklet that has complete German texts but no translations (Audite 23.416, two discs, 1 hour 37 minutes).

A set of Knappertsbusch's RIAS recordings with the Berlin Philharmonic includes two performances of Bruckner's Ninth Symphony and Schubert's 'Unfinished', along with the Eighth Symphonies of Bruckner and Beethoven and Haydn's 'Surprise', No. 94. There's also lighter repertoire: the Overture to The Merry Wives of Windsor by Nicolai, the Nutcracker Suite by Tchaikovsky, A Thousand and One Nights, the Fledermaus Overture and Pizzicato Polka by Johann Strauss II and Komzák's Bad'ner Mad'ln. Audite has used original master tapes, so these performances sound as good as they are ever likely to: for 1950-52 it's very acceptable. Knappertsbusch can be quirky in Bruckner: in the Eighth, a variable pulse often saps the music of momentum, especially in the finale, and there's a problem with the edition too: the 1892 first edition, despite the apologia in the booklet, is extensively reorchestrated and somewhat bowdlerized. This wouldn't matter if Knappertsbusch's 1951 performance was more compelling, but it's rather mannered and clumsy. The Ninth is vastly better, both in the studio performance and the live one two days later: the first movement has a powerful undertow, never drags and has climaxes that are visionary, while the finale is both anguished and majestic.

The Beethoven is interesting: while it's all on the steady side, the first movement is particularly well shaped and there's no shortage of geniality. The Haydn is similarly good-natured. The two performances of the 'Unfinished' are surely too expansive in places – so much so that even the orchestral cellos and basses seem to want to get a move on near the beginning. The lighter music is most enjoyable. The Nutcracker is nicely poised and even though the 'Waltz of Flowers' sounds as if it's going to be rather stately, Knappertsbusch whips things up by the end. The Fledermaus Overture that follows is bursting with charm and it's enormously enjoyable, and so too is The Merry Wives of Windsor – these are probably my two favourite performances in a set that is always fascinating, and presented with Audite's customary care (Audite 21.405, five discs, 5 hours 55 minutes).

Entitling this record 'Leoš Janáček: complete string quartets', as Audite does, looks rather odd when he wrote only two. The simple explanation is that we have three performances here: the First Quartet ('after L. N. Tolstoy's 'Kreutzer Sonata") and the Second Quartet in two versions, one with the traditional four instruments, the other with viola d'amore replacing the usual viola; but things are a bit more complicated than that.

In 1903, on one of his summer visits to the spa of Luhačovice, Janáček met Kamila Urválková. She had already been the subject of an opera, Kamilla, by, so to speak, a previous relationship with another composer, Ludvík Čelanský, in which to her irritation she was portrayed as an air-headed little flirt. The susceptible Janáček was immediately smitten. 'She was one of the most beautiful of women', he declared in his autobiography (from photographs, one can see that he had a point), adding, 'Her voice was like violas d'amore.' He had come upon the viola d'amore in Berlioz's treatise on orchestration, where its tone is described as 'faible et doux', suitable for 'I' expression des sentiments extatiques et religieux', and he had heard it in a work that much influenced him, Charpentier's Louise. When he then set to work on a new opera, Fate, all about the composition of an opera in a spa, the heroine 'Míla', which also means 'dear', was associated with love music on the instrument (he used it similarly in Kát'a Kabanová, and elsewhere, as can be heard in Charles Mackerras's recordings).

So it was primed in his imagination for the association with Kamila Stösslová, another Luhačovice encounter, the muse of his late years and the subject of the Second Quartet. This was originally subtitled on the autograph sketch 'Listy milostné', 'Love letters': only later came the more discreet title 'Listy důvêrné', usually translated as 'Intimate letters' but better really the more elliptical 'Confidential letters'. Originally, the instrument at the centre of the quartet was to be the viola d'amore; but when the Moravian Quartet came to play the work through to Janáček, he was forced to concede that the instrument was impracticable and reluctantly cut it out. As John Tyrrell sagaciously puts it, in a sub-chapter on the viola d'amore in his Cambridge Opera Handbook on Kát'a Kabanová (Cambridge; 1982), 'While there is much to be said for authentic recordings with the viola d 'amore included ... in general we should regard the instrument as one of the inspirational devices which helped Janáček to compose.'

We live, of course, in an age of 'authenticity', which is also an age of many paradoxes, as when Mackerras candidly admits that with the viola d'amore in Kát'a, ‘Modern recording ... has made it possible to realise [Janáček’s] intention to the letter.' This is less necessary with the string quartet. 'Authenticity' is handsomely served by the viola d'amore player, Gunter Teuffel, using the actual instrument owned by Rudolf Reissig, who taught at Janáček's Organ Conservatory from 1903 to 1909. Pictures show a beautiful instrument, with a broad belly and bridge to accommodate the seven playing strings as well as the seven resonating strings which provide the characteristic halo of sound. The opening solo, however, is partly inaudible. This makes it odd to have chosen to overshadow it by using the opening chordal theme in the powerful version for bowed strings, rather than the lighter pizzicato (there are other differences, deriving from issues with the manuscript and parts). Pizzicato was used on the only previous record with the viola d'amore, clearly played by John Anthony Calabrese with the Kubin Quartet as part of Volume 4 of the fascinating 'The Unknown Janáček' Supraphon series. Later in the movement on the new recording, the molto meno mosso sounds well, and on the penultimate page the adagio solo, singing through carefully disposed chords from the other strings, is beautiful. Similarly, the opening solo of the second movement is sweet and clear, the instrument holds its own in the lilting moderato, and in the finale adds a fascinating colour to the elaborate textures at the espresso section (Fig. 12). There are further complexities of version, it should be added, too complex to be pursued here, as Janáček modified the score. The seriously curious should consult the text published in 2009 as part of the ongoing Janáček Complete Edition.

What of the actual performances? In the First Quartet, the music is very well phrased, with smooth and well-blended tone, though there is some lack of menace, of the sense of living on the edge of an abyss in this reflection of Tolstoy's threatening story. Emotions that are barely controlled can sound too controlled here, and it is part of Janáček's idiom for there to be sudden outbursts that are far from tame. A comparable smoothness marks the playing in the Second Quartet, a sense of emotions running easily and comfortably rather than with such urgency that they have to be held fiercely in check, which is part of the whole situation that led to Janáček composing the work as he did. There are stronger, more urgent performances from the Skampa and Panocha Quartets, not to mention the classic old version by the Talich Quartet, and indeed the excellent Janáček Quartet. Yet for Janáček collectors, this is of course an enthralling disc, and one to engage the attention of anyone gripped by the passionate, even violent interactions of Janáček's life and his music.

I point out to Wunderlich fans that Audite has released a CD of Stravinsky's Perséphone, with the tenor in his only appearance as the priest Eumolpius. The actress Doris Schade is Perséphone, with Dean Dixon conducting, in a live Frankfurt performance. The work's première was at the Paris Opéra in 1934, with Ida Rubinstein, who had commissioned it, as Perséphone and René Maison as Eumolpius. Wunderlich is in his best voice, steady, focused, noble, but has little to sing. Collectors interested in him rather than the work may want this disc for the sake of a new title in his discography (Audite 95.619, 49 minutes).

If ever there were a conductor whose work often confounded expectations, it was the German conductor Hans Knappertsbusch. Commonly daubed a Teutonic slow-coach, "Kna" (as he was known) proves to have been anything but a slouch, especially in that popular haven for slouches of the baton, Anton Bruckner. Audite's five-disc collection of "The Complete RIAS Recordings" includes Knappertsbusch's Berlin Philharmonic versions of Bruckner's Eighth (1951) and Ninth (1950) symphonies, the latter presented in two versions, just days apart, one studio-recorded, the other live ... and what a difference! The fact that the live version features a broader Adagio is of marginal interest but more to the point is its highly charged atmosphere and the added intensity of the string playing. The finale is surely one of the great recorded Bruckner performances, in spite of some interpretative (editorial?) peculiarities (a "Gates of Heaven" episode that rockets from ppp to fff and an abrupt final chord for the last tortuous climax). Both symphonies approximate, in Knappertsbusch's hands, the billowing storm clouds of Wagner's music dramas and bring the music newly to life, though collectors versed in Bruckner scholarship might balk at the editions used. There are also two versions of Schubert's Unfinished, again quite different in detail (Knappertsbusch plumbed the depths of this piece just as Furtwängler did), as well as an affable Haydn Surprise Symphony and a gruff though solidly built Beethoven Eighth. As for the lighter fare (The Nutcracker Suite, Otto Nicolai, Johann Strauss II, Karel Komzák II), Knappertsbusch certainly knew how to relax, though never to the extent of losing the shape of a piece. It's here more than in the classics that we smile at his fat textures, broad tempi and warmly arched phrasing, his humanness, which makes this set such a pleasure to dip into.

Although recorded a few years later, "Sir John Barbirolli in New York" (1959) isn't quite so pleasing, sound-wise, though the pleasure of hearing Richard Lewis, Maureen Forrester and the less familiar Morley Meredith enter fully into the spirit of Elgar's The Dream of Gerontius soon banishes any doubts about the variable sound quality. The Introduction and Allegro is given a big, broad reading, weighty and impassioned, and there's a suite of five movements from The Planets, opening with a particularly gruelling "Mars". A warm-hearted Mahler First Symphony has already been released as part of the New York Philharmonic's Mahler symphony collection (1/99), and there are chunky and communicative versions of Brahms's Violin Concerto (with Berl Senovsky), Haydn's 88th, Vaughan Williams's Eighth and, least appealing perhaps, Barbirolli's own Elizabethan Suite. But the Elgar items are surely essential listening for all fans of this great conductor.

The Barbirolli Society's own sizeable catalogue includes a good number of New York Philharmonic broadcasts but their latest programme hales from the Royal Albert Hall, a Prom, again from 1959, featuring Tchaikovsky's Fourth Symphony in a performance that marries the expected warmth (how lovely to hear those cello portamentos in the Andantino) with an imposing level of drama: the climactic moment in the finale where the opening fanfares return is mind-bogglingly powerful. The programme also includes the first UK performance of Bohuslav Martinů's Oboe Concerto, H353, with Lady Barbirolli as soloist, a performance that also haunts the memory.

Barbirolli's 1959 Tchaikovsky/Martinů recordings are in mono but Pristine Audio have recently achieved the unimaginable by releasing Arturo Toscanini's hair-raising 1951 NBC Verdi Requiem in stereo. What we have are two separate recordings with independent microphone placements, and the result, although strictly speaking not stereo in the "two-track tape" sense of the term, does allow for some directional information – which is especially noticeable in the choral singing and the echoing trumpets in the "Tuba mirum". The one trivial disappointment is that Toscanini's urging shouts, which were such a thrilling component on the dry, mono RCA transfer (12/56), are inaudible. True, there is some vinyl surface noise and some minor clouding of detail, but the effect is still pretty stunning, a version to own alongside RCA's straight tape transfer I'd suggest, an added dimension rather than a replacement. Toscanini's vocal line-up for 1951 was Herva Nelli, Fedora Barbieri, Giuseppe di Stefano and Cesare Siepi, whereas for his 1940 NBC broadcast he chose a partially superior team consisting of Zinka Milanov, Bruna Castagna, Jussi Björling and Nicola Moscona. The 1940 performance, another excellent transfer, is broader and tighter than the one from 1951, and the vocal team is very much dominated by Milanov and Björling. Sound-wise, the balance engineers thrust the singers in your face, but given the overall quality of the singing, who's complaining? Both performances stand head and shoulders above most recorded rivals. The 1940 set also includes Toscanini's NBC broadcasts of Verdi's original, discarded Aida Overture (exciting but no masterpiece) and Castelnuovo-Tedesco's attractive Taming of the Shrew Overture.

Toscanini's 1943 English-language NBC relay of Brahms's German Requiem (with Vivian della Chiesa and Herbert Janssen) is both warmly phrased and, in the mighty second movement (taken very slowly), extremely imposing. Mediocre transfers have come and gone, some with hum and distortion, but Pristine achieves a cleaner, fuller sound than most, so that we can appreciate this elevating interpretation afresh.

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