Prism I opened the five-album series in which the Danish String Quartet sets each of Beethoven's late string quartets between a Bach fugue and a later work linked to it. Here the common ground is the key of E-flat. Bach's Fugue BWV 876, in Mozart's arrangement for strings, leads into Shostakovich's last quartet, No. 15 in E-flat minor, and the programme ends with Beethoven's Op. 127 in E-flat major, the first of his late quartets.

This was the group's third ECM album, after a 2016 New Series disc of Per Nørgård, Hans Abrahamsen and Thomas Adès and the folk collection Last Leaf (2017). The players are Rune Tonsgaard Sørensen and Frederik Øland, who share the first violin chair, violist Asbjørn Nørgaard and cellist Fredrik Schøyen Sjölin. Sørensen leads in the Shostakovich, Øland in the Bach and the Beethoven. The recording was made in November 2016 at the Reitstadel in Neumarkt, with Markus Heiland as engineer and Manfred Eicher producing. The quartet wrote part of the booklet notes, alongside the critic Paul Griffiths.

The quartet has said that late Beethoven first felt "as if it had fallen down from outer space onto our music stands", and the sequence tries to restore that strangeness. The short Bach fugue, written for keyboard in Book II of The Well-Tempered Clavier, sets a calm, contrapuntal opening. Shostakovich's Fifteenth (1974) follows as six slow movements, from the long opening Elegy to the Funeral March and Epilogue, played with very little vibrato. Its close in E-flat minor turns directly into the major-key Beethoven, whose central Adagio is a long set of variations.

The album was nominated for a Grammy in the Best Chamber Music/Small Ensemble Performance category at the 2019 awards. Writing in Gramophone, Richard Bratby found the playing "exquisitely refined" yet never without a sense of rhythmic danger, and found the readings thought-provoking. Fiona Maddocks in The Observer heard a group that "plays with virtuosity, intensity and tenderness". Dominy Clements of MusicWeb International (2018) heard the Beethoven slow movement as the high point, and noted that the sparing vibrato in the Shostakovich costs nothing in expression. James Manheim of AllMusic praised the spacious, quiet acoustic ECM's engineers drew from the Neumarkt hall.

This is the CD edition, ECM New Series 2561, first released on 21 September 2018, with a 28-page booklet including photographs of the composers' manuscripts.