According to Official Guinness Records,
The greatest distance between people singing a duet is 12,120 km (7,531 miles) and was achieved by Shân Cothi (UK) and Andres Evans (Argentina), for BBC Music Day 2015, in Cardiff, UK and Gaiman, Argentina, on 5 June 2015. Shân and Andres performed Calon Lân, a Welsh hymn. They were supported by the BBC National Orchestra of Wales, Cor Radio Cymru, The Wales Millenium Centre/Only Kids Aloud Chorus and Cor CF1 in Cardiff and the choir Cor Tsgol Gerdd y Gaiman in Argentina. The duet was part of the first BBC Music Day and also marks the 150th anniversary of the first Welsh settlers arriving in the Patagonia area of Argentina. The singers worked to a ‘click track’ to keep them in time with one another. Both sides of the duet came together live in the control room in Cardiff.
For a complete list of 2015 records, please visit 2015 Guinness Records in United Kingdom.