The clavichord was a very simple instrument of keys and strings. The length of the vibrating string (which determines its pitch) was set, at the stroke which set it in vibration, by a metal ‘tangent’ on the end of the key lever, being at once the hammer and the fret of the string. The stroke was slight, the tone was extremely soft. The vibration continued only a few seconds and was so slight that anything like the ‘singing tone’ of the pianoforte was impossible. But within the duration of a single note the player, by a rapid upward and downward movement of the wrist which varied the pressure on the key, could produce a wavering tone similar to the vibrato of the human voice and the violin, which gave a faint but live warmth to the tone, unhappily wholly lacking in the tone of the pianoforte. It was doubtless this peculiar ‘live’ expressiveness which made the instrument a favorite of the great Bach, and which, moreover, justifies the player in making the utmost possible variety of tone in playing Bach’s clavier works on the modern instrument. The sound of the instrument was something like that of an æolian harp, and was therefore quite unsuited to the concert hall. But it was of a sympathetic quality that made it a favorite for small rooms, and much loved by composers for their private musings.
The harpsichord was the concert piano, so to speak, of the time. Its strings were plucked by means of a short quill, and a damper automatically deadened the tone an instant afterwards. The instrument was therefore quite incapable of sustained melody, or of gradations of volume, except with the use of stops, which on the best instruments could bring new sets of strings into play. Its tone was sharp and mechanical, not very unlike that of a mandolin.
Now what the modern pianoforte possesses (apart from its greater range and resonance) is chiefly ability to control the power of the tone by force or lightness of touch, and to sustain individual notes, by means of holding down the key, or all of them together through the use of the sustaining pedal. Theoretically, the clavichord could both control power and sustain notes, but the tone was so slight that these virtues were of little practical use. The ground principle of the pianoforte is its rebounding hammer, which strikes the string with any desired power and immediately rebounds so as to permit it to continue vibrating. Each string is provided with its damper, which is held away from it as long as the key is pressed down. The sustaining or damper pedal removes all the dampers from the strings, so that any notes which are struck will continue vibrating. The one thing which the piano cannot do is to control the tone after it is struck. By great care in the use of materials piano makers have been able to produce a tone which continues vibrating with great purity and persistence, but this inevitably dies out as the vibrations become diminished in amplitude. The ‘legato’ of the pianoforte is only a second best, and is rather an aural illusion than a fact. Any increasing of the tone, as with the violin, is quite impossible. Any true sustaining of the tone is equally impossible, but, by skillful writing and playing, the illusion of a legato tone can be well maintained and a far greater beauty and variety of effect can be reached than one might think possible from a mechanical examination of the instrument.