There is an indication at the beginning of Mozart’s K. 421 for the performers to play ‘sotto voce’ – under the voice or hushed. I like to think of Mozart hunched over his clavichord – the softest and most subtle of keyboard instruments – composing such music.
D minor is the key of K. 421; the same key as his Requiem. This quartet is a beautifully balanced work. Despite the D minor basis, there is as much lightness as melancholy because of Mozart’s use of different keys.
Why do composers choose particular keys for the pieces they are composing? Sometimes it is for practical reasons based on the combinations of instruments in the ensemble. Generally it seems a more intuitive choice. It is possible that for some composers it is linked to synaesthesia – the way sounds evince certain colours in the mind of the listener, the colours relating to feelings and moods.
For performers, all keys have a particular physical sensation in the hand so the sensation of playing in a certain key is decidedly visceral. The choice of key by the composer becomes a physical experience for the performer and in live performance this is arguably partly transmitted to listeners. We all feel the key, its colour and character.
We love playing this piece. It always feeds the soul.