So little documentary evidence remains of Bach (many of his major works are still lost without trace) that the survival of his seven harpsichord concertos assumes great significance. From these works, we can learn much about scoring that elsewhere has had to be conjectured; their origin as concertos for violin or oboe adds to the fascination. Until Bach put it in center stage, nobody had thought of the harpsichord as a solo instrument: it was with these works that a new genre came into being that would culminate in the concertos of Mozart and Beethoven. And they still dazzle today. Naxos's battery of soloists, led by the musicologist Robert Hill, is extremely good, working up exhilarating miasmas of sound above the accompanying orchestra. But this orchestra embodies the concept of historical practice on modern instruments, which raises all sorts of questions. In both pitch and tone quality, they are irredeemably modern: the "period" element is somewhat elusive.