I remember the first time I ever played Bach seriously, when at school we performed the fifth Brandenburg Concerto. I was revelling in the experience of playing in a small chamber group for the first time and loving the baroque cleanness of it all, when I was overwhelmed by the harpsichord cadenza to the first movement. It still never fails to astonish, the way it starts simply and then builds through rhythmic and harmonic complexity, exploiting the instrument's versatility to the full (again …