There is no need to say anything about 'The Well Tempered Clavier', even though judging here from some reviewers' mystification over the clavichord, they seem to think there is some connection between 'clavier' and 'clavichord': there is not. 'Clavier' is the English spelling for the German 'Klavier', or, 'keyboard'; 'clavichord' happens to be the ancestor to the piano, for it is a keyboard instrument whose strings are not plucked (like the harpsichord) but are struck with metal pedals, thus allowing for dynamic shading. The nature of the pedals gives its 'metallic' sound, and, the instrument's extremely soft sound - too faint for a concert hall - is due to its size and structure.
The clavichord also happens to have been Bach's favorite instrument and is a revelation for anyone who hasn't heard this rarely played instrument. Naturally, it requires some acclimatization, because the tone is not unlike Glenn Gould's jocular description - "a castrated piano". But wisecracks aside, the clavichord's sound shall delight the most refined palates.
Ralph Kirpatrick's magisterial rendition evinces the instrument's potentialities. For example, the D-sharp Minor fugue from Book I is particularly suited on the clavichord due to its frequent restatements of the theme in all its V voices in various registers, which can only be properly highlighted by dynamic emphasis, which is obviously impossible to do on the harpsichord without changing the sound far too substantially, using the lute-stop. Another superb example of the clavichord's suitability for the WTC is the E-flat Minor Prelude from Book I, which in this reading is of particular intensity, due to its sound's sincerity in characterizing authentic despair. But to enumerate the treasures of this recording would be tiresome. Let it suffice to say that this recording is outstanding and is a perfect complement to Kirpatrick's other recording of 'The Well Tempered Clavier' on the harpsichord, which sadly has never been issued on CD. Kirpatrick was a great scholar, but also a great musician; and anyone who reads his notes of his edition of the score of 60 Scarlatti's sonatas published by Schirmer shall gather the depth and sensitivity of his musicianship.
This recording of Bach's masterwork is a landmark of twentieth-century recordings.