B. Britten, Requiem, Shafer, The Washington Chorus, NSO
The Mass itself is a bit of a musical quilt. Composed over 24 years, it was at least not conceived from the beginning to be a cohesive whole. Nikolaus Harnoncourt (who also put the Mass on disc in a milestone recording with the Concentus Musicus Wien) discusses origin and performance practice at length in his book Der musikalische Dialog (available in English on Amazon.)
Robert Shafer mentions our (relatively) new understanding of the performance of the Mass (he refers to Mr. Harnoncourt's recording in his liner notes) and explains that the ultimate goal in presenting Bach's work (who himself never heard it performed) is getting the balance right. In order to do that with a modern orchestra, a bigger choir is needed. If that necessarily means eight times bigger than Bach would have had is a different matter, it seems. "Advanced choral art," meanwhile, helps keep the textures as clean as they would have been in Bach's day.
What exactly "advanced choral art" amounts to, I do not know, but I am happy to report that the choir did sound darn good. That the textures were as clean as in the old days (assuming that is even desirable) is not likely to be true... in fact could not have been true with the orchestra playing vibrato like it's Mahler.
J. S. Bach, Mass in B Minor, Gardiner
The singing was faultless, with the small exception of the "Crucifixus etiam pro nobis" part of the Credo, where the pianissimo parts fell apart and became a cluster of soft hisses flying about, like the flashes going off in the bleachers at a sporting event. Minor quibbles, indeed, and hardly reason not to treat oneself to a live account of this wonderful work that will always carry a special appeal to experience in person.
J. S. Bach, Mass in B Minor, van Veldhoven (nla)
My favorite available recording of the B Minor is van Veldhoven's (Gardiner, Rilling, , while Karajan with Kathleen Ferrier is an interesting (and in its way rather impressive, mostly because of her), obviously more old fashioned versions. A disc with excerpts of it (as well as the complete, also Ferrier-wonderful 1950 St. Matthew Passion, recently reissued and remastered by Andante) is readily available. Karl Richter, as great a Bach conductor as there ever was, has his performances see the light of day again in a 10-disc collection by Archiv of all the sacred works by Bach. (Gardiner, too, had his Bach Passions and Masses reissued a few weeks ago... and if you were thinking about getting even just one more of his Bach recordings of the Passions (or the Christmas Oratorio [my favorite being Richter]), it is worth getting the whole set.)