Liszt’s output exists in a state of flux, since many of his works (especially his songs) appear in multiple versions. Sometimes he was aiming for refinement but often he was exploring the material from different angles. In these cases, the essence of the piece is found not in its final revision but in the sum of its variants. Just as seeing the two images of a slide together through a stereoscope (wildly popular in the mid-19th century) provides a visual depth that neither image has on its own, so hearing Liszt’s multiple alternatives provides an aural depth.

The orchestral versions of these songs – four of which are getting their first recordings – provide depth of a particular sort. You might expect Liszt to have seized the opportunity to rethink the substance of the music. But the adaptations hew closely to their models, even ‘Die Vätergruft’, where nearly 40 years separate the original from the orchestration (perhaps his last completed work). Yes, there are new ornaments, adjustments in the shape of vocal lines, enriched accompaniments and added interludes (especially in ‘Die drei Zigeuner’, where, taking off from his transcription for piano and violin, he gives the solo violin a chance to shine), but the music’s basic profiles remain intact.

No, the alternative perspectives here come not from recomposition but from emotional heightening, often with a Wagnerian tint. The prelude to ‘Die Lorelei’ (second version), presaging Tristan, sounds even more poignant when clothed in string sounds; ‘Die Vätergruft’ takes on a glower reminiscent of Götterdämmerung. This intensification is especially valuable in the least familiar songs here. ‘Der Titan’, an ode to defiant will that’s generally catalogued as an abandoned choral work, is slightly flat in black-and-white. But the orchestration (done with the help of August Conradi) draws out stirring melodramatic power. ‘Weimars Toten’, a potentially turgid tribute to great German poets of the past, reveals a proto-Meistersinger spring in its orchestral form (in this case, there’s some debate about which version came first). The only work not enhanced by the orchestration is ‘Le Juif errant’. It’s an obsessive plaint that Liszt also decided not to publish; in this version, it sounds more like a drinking song than a rant against human cruelty.

The same respectful intensification marks his orchestrations of Schubert songs, five of which (with another first recording) are also included. Liszt can sometimes be a vulgar orchestrator. Not here: his decision to silence the timpani until near the end of ‘Erlkönig’ is an elegant dramatic stroke, just as the gentle repeated horns in the background of ‘Gretchen am Spinnrade’ give an extra shimmer of sinistrality with exceptional tact.

Thomas Hampson’s voice has held up well, and his rhetorical acumen keeps us transfixed. The other singers are similarly well matched to the music. Stephanie Houtzeel braids the seductiveness and mournfulness of ‘Die Lorelei’ perfectly; Sunhae Im has the radiant purity and innocence her three songs require; and in ‘Der Titan’, Tomasz Konieczny, an experienced Alberich and Wotan, rages with overwhelming power. Conductor Martin Haselböck and the period-instrument Vienna Academy Orchestra, who have done so much to recapture the original sound of Liszt’s orchestral music, deliver perceptive and often striking support: the snarling string opening of ‘Erlkönig’ hits you like the beginning of Mahler’s Second Symphony. The engineering is excellent.

Unfortunately, despite the obscurity of some of the poetry, there are no texts or translations. Other than that, this revelatory release is near perfect.