Performances of Claude Debussy’s only opera Pelléas et Mélisande at the Metropolitan Opera have been almost as elusive as the frail, mysterious Mélisande herself. Since its first Met performance on 21 March 1925, just a mere 23 years after its world premiere, the opera has only been performed 114 times to date. That’s a total of 93 years. To put that into context using the ABCs of the opera world, Aïda, La Bohème and Carmen, each reached their 114th performances 21, 12 and 15 years after their first performances at the Met, respectively.

This live broadcast recording from the stage of the Met dates from the very end of 1962, the last of a run of five performances conducted by Ernest Ansermet, of whom the New York Times wrote: "Naturally he was the hero of the evening. ‘‘Pelléas et Mélisande” is a conductor’s opera, and it demands the services of a man who is a precise stylist and a precise technician. Despite its seeming economy of means, “Pelléas et Mélisande” is very difficult to conduct. Textures must be transparent; the score is a cobweb of sound, seldom arising above a mezzoforte. At that, Mr. Ansermet released his forces more than do most conductors, and the opera last night seemed to have a little more red blood in it than usual."

With George London as Golaud and Nicolai Gedda and Anna Moffo in the title roles, this is a classic performance of a ground-breaking opera.

You'd perhaps imagine that just about everything Rudolf Serkin's recorded has been unearthed and released by now, but that's not the case. Mark Obert-Thorn has restored two previously unpublished recordings from early in his career, including a full performance of the Schumann Piano Concerto with the London Philharmonic Orchestra under composer Julius Harrison from 1936.

Also out for the first time is a recording with the great Adolf Busch. Together they tackle Busoni's second Violin Sonata in a US broadcast from 1940. As Tully Potter explains in his notes, the pair were hugely informed and influenced in their interpretation by meetings with the composer and bearing witness to his own performance of the work.

Finally there's Serkin's justifiably famous 1936 studio recording of Beethoven's Appassionata Sonata. For a recording which stayed in print for decades you may be surprised to learn that it had fallen out of circulation. Furthermore, all previous CD reissues of it derived from a flawed transfer that omitted a chord - so this is actually the first time the whole recording has appeared in a digital format!