The Prince Consort/ Grevelius/Johnson, Wigmore Hall, London<br>CBSO/Kamu, Symphony Hall, Birmingham<br>LPO/Elder/Coote/Nilon, Wigmore Hall, London

Two sets of waltzes for voices and piano reveal aspects of Brahms he may have wished to hide

It's odd how sexless Brahms's image is in the popular imagination: a portly, bearded, indignant old man standing firm against the sensory incontinence of Wagner and Liszt. Lip-bitingly handsome in his youth, addicted to prostitutes and serially attracted to women he would not or could not marry, the composer who gazed at female musicians "as a greedy boy stares at jam tartlets" was hardly a stranger to sex. But how startling to hear the shift in tone between the light flirtations of the Liebeslieder-Walzer of 1869 and the calcified cynicism of the Neue Liebeslieder-Walzer of 1874.

Written at the height of the fad for piano duets, both sets of waltzes were published for four hands with a view to being bestsellers. But aside from Brahms's decision to conclude the second collection with Goethe's valedictory "Zum Schluss" – in which the writer renounces love, and the composer hints at his own Requiem setting of "Wie lieblich sind deine Wohnungen" – there's a fundamental change in the music and poetry. The waltz's country cousin, the ländler, acquires brutal vigour in the later songs, while the innocent young lovers have become predatory vamps and "worthless young men".

Performed by The Prince Consort, mezzo-soprano Anna Grevelius and veteran lieder-accompanist Graham Johnson at the Wigmore Hall, both cycles were potently seductive. From the lilting quartet "Rede, Mädchen", through the joshing locker-room duet "O die Frauen" to soprano Anna Leese's gleaming "Wohl schö*bewandt", the Liebeslieder-Walzer were brilliantly contrasted and characterised. If Leese, pianist Alisdair Hogarth, tenor Andrew Staples and baritone Jacques Imbrailo haven't pressed Grevelius to join them permanently, they should. Stylistically and tonally, the blend was sensational.

Hogarth's articulation of the brief selection of Schumann duets sparkled, though soprano Sarah-Jane Brandon remained subdued. Grevelius' and Imbrailo's "Ich bin dein Baum" was lovingly phrased, while Leese and Staples sparred merrily in the hokey Burns setting "Liebhabers Ständchen" before tumbling into the violent amorous skirmishes of the Neue Liebeslieder-Walzer. Here it was all flashing eyes and poisoned hearts – much of the poetry is concerned with gazes, glares and glances – and the bitter betrayals of "Alles, alles in den Wind" and "Schwarzer Wald". A vivid, compelling performance, and one that betrayed more of the composer's character than he could have planned.

My attempt to understand the appeal of Nielsen, who seems to me a proficient rather than inspiring composer, is still work-in-progress after hearing Okku Kamu's proficient rather than inspiring performance of Helios and the Second and Sixth Symphonies with the City of Birmingham Symphony Orchestra. I return to Birmingham for the last of the CBSO/Hallé Nielsen series next month. But this week I'm sticking with chamber music, or music that can, at a squeeze, be done as chamber music.

I've often wondered whether Cosima Wagner's rapturous diary entry on waking up to the Siegfried Idyll on Christmas Day 1870 was written in the expectation that her husband would read it. Last Friday's performance by members of the London Philharmonic Orchestra at the Wigmore Hall conjured something of the surprise of hearing it in a domestic setting: the intimacy, the oddness, the loudness. For although you can fit 13 players on a quartet-sized stage, you can't make them balance. Add in the tam-tam, harmonium, celesta, percussion, conductor and two singers for Schoenberg's arrangement of Das Lied von der Erde and it's less a concert than an attempt to get into Guinness World Records.

Distorted though the balance was, and constrained as conductor Mark Elder's movements had to be, there were some wonderful moments: Paul Nilon's biting top notes in "Das Trinklied von Jammer der Erde", the cartoon frenzy of Schoenberg's orchestration in "Von der Schönheit", and Alice Coote's supple spinning of the repeated "Ewig... ewig...". Nonetheless, even reduced Mahler needs a bigger space than this. As to the Siegfried Idyll, I'd still rather wake up to a cup of coffee.