Bach Collegium Japan, conducted by Masaaki Suzuki, its founder, conductor and music director.
It wasn't a piece I was familiar with, but I thoroughly enjoyed it. I was told by my companion on that evening, who used to sing in a choir, that Suzuki was conducting the Mass really slow, and that it must have been very hard for the singers. She also said that normally this Mass is sung by a choir of a hundred - we only counted 18 or 19 singers, including the soloists (who were all Western, strangely enough). I didn't notice any of these subtleties of course, as I had only listened to the first half hour of it on Deezer the night before.
What I did notice however, was how clearly every voice, every instrument, shone through. It was an amazing experience - Bach is not as rhythmic as Handel - no sing-along Hallelujah or For Unto Us A Child Is Born here. But a feeling that every note counted.
That's the joy of live music
(Picture from Alix Pochribniak via Twitter)
And here are links to the full Mass on YouTube - Embedding was disabled, so when you click on these, you will be brought to YouTube.