Christian Gerhaher [Nikolaj Lund]

ASKED what it takes to sing the taxing, long-duration works of Wagner, the soprano Birgit Nilsson famously replied “a comfortable pair of shoes”: a musical accessory that may also prove useful for anyone who signs up for a strange Festival Hall premiere on April 30. Because it involves the audience walking through the streets of London to the venue.

Devised by composer Huang Ruo, City of Floating Sounds asks you to choose a starting-point and download a smartphone app – which will (a) start playing music, and (b) hook you up with other people nearby, who then join you walking to the Hall where the full piece gets played by the BBC Concert Orchestra.

If that sounds like something between online dating and chaos, it could well be both. But interesting. Full details: southbankcentre.co.uk

• Nilsson’s footwear advice is also timely in that the next instalment of the Royal Opera’s new Ring Cycle opens May 1. It’s Die Walkure, a notoriously big sing for the performers who include Christopher Maltman as Wotan and Natalya Romaniw as Sieglinde. Antonio Pappano returns to his old fiefdom to conduct. Runs to May 17. rbo.org.uk

• Expect the classiest singing of the week to come when Christian Gerhaher – one of the great vocal recitalists of our time – continues his journey through Schuman’s songs at Wigmore Hall, April 27. But for an introduction to great voices of the future (maybe) the Wigmore also holds the finals of the prestigious Kathleen Ferrier Competition, April 25. And if you want to take a sleeping bag, you might as well be at the Hall for April 26 as well, when cellist Sheku Kanneh-Mason and his pianist sister Isata play Faure and Poulenc. wigmore-hall.org.uk

• The keyboard event of the week, though, will be Stephen Hough’s appearance at the Barbican, April 25, playing Beethoven’s 3rd Concerto with the BBCSO. Also on the bill is Mahler’s sparkling 1st Symphony. barbican.org.uk

• And for an example of heavier Mahler, his 8th Symphony – known as Symphony of a Thousand because it packs so many people on the platform – gets a Southbank performance from the LPO, April 25. What’s more, it’s announced as “semi-staged”– though what that means is anybody’s guess because the Festival Hall has given few details and it’s hard to know how this piece can be staged. Or why. southbank.org.uk

• One of my favourite living American composers is Jennifer Higdon whose orchestral masterwork Blue Cathedral gets done by the ensemble Outcry at Smith Square, April 27, alongside Britten’s Violin Concerto and Tchaikovsky’s 5th Symphony: an odd grouping, justified by Outcry on the grounds that all the composers are gay. You might be tempted to say So what? But they’re all worth hearing. sinfoniasmithsquare.org.uk

l Finally, the Carducci Quartet with whom I’ve just been on a trip to Cremona where the world’s most coveted string instruments tend to have been made. They were playing Shostakovich – magnificently – in the violin museum there. And they’re playing more Shostakovich, April 29, as part of their ongoing series at London’s Milton Court. On the bill is the enlarged version of the composer’s 8th quartet that gets billed as a “chamber symphony” – for which they’re joined by players from other quartet ensembles in a sort of chamber-music lovefest. barbican.org.uk