Most of Bach's keyboard output is 'instrument neutral', meaning that it can be played on any available type of keyboard instrument: harpsichord, clavichord, fortepiano, or organ; but some pieces call for specific instruments either explicitly (the organ sonatas of Wq 70, or the "Bogenclavier" sonata, Wq 65/48) or implicitly (pieces that call for Bebung
and other clavichord-specific techniques).
Thus the challenge is not so much to produce yet a nother Ninth, this time more in tune with HIP, but rather to appreciate Carl Philipp Emanuel Bach's Bebung
, Clementi's legato, and portamento in Louis Spohr's Fifth, not to mention the tempo rubato of Willem Mengelberg's Mahler.
Christopher Hogwood presents a survey of late eighteenth-century works prescribing the use of Bebung
, the vibrato possible on the clavichord alone among keyboard instruments, and the related portato or Tragen der Tone.