History of harpsichord music
The harpsichord flourished during the Baroque era. Starting in about 1600, an original member of the harpsichord family was standard in most western music, its direct ancestor being the clavicymbalum (or keyed hammer). It was around this time that northern German composers started making use of the instrument in their scores, while elsewhere in Europe it remained silent except in the hands of keyboard virtuosos throughout much of that same century.
The first mention of a cornetto-like pair of pipes with keyboards known to be associated with one player at the court of Bavaria may date from 1604. The next description well documented is an illustration found on 1607 set by Jacob Hochbrucker, in which a keyboard player is seen to play something that resembles a small harpsichord. With the spread of the instrument to France and England by 1660, Italian players became commonly known in music circles throughout Europe.
In the 18th century, the harpsichord was gradually supplanted by the piano, which had been invented by Bartolomeo Christophori in Florence in about 1709. Harpsichords were made with one or more sets of strings called choirs or ranks. A typical three-register harpsichord has two sets of strings sharing one keyboard called manuals, while some special instruments have additional sets of strings or extra keyboards on separate manuals referred to as jacks.
The entire instrument is called a consort or virginal, and each set of strings or rank is termed a stop (or sometimes coupler ). The basic principle behind the harpsichord's action, known as hand-to-hand, was also used in virginals and spinets, and while it was not at first universal on clavichords it became so by the mid-18th century.
Harpsichords were made without dampers. When a key was pressed, the jack would immediately pluck the string(s). If this key were held down continuously and additional notes were played, all notes would sound continuous until keys were released. This effect is commonly heard in Baroque music written before about 1750: although the notes are played intermittently, successive individual notes rather than chords are almost always preferred; resulting in an effect similar to that of harp arpeggios.
For this reason, repeated notes or chords were usually short and detached (i.e., staccato), not sustained for their full value (legato). The clavichord was the keyboard instrument that offered Bach the greatest expressive possibilities in composition.
History of piano music
The piano was invented in Italy at the end of the 18th century by Bartolomeo Christophori. It was based on existing ideas about the string instrument family, especially Cristofori's pianofortes. Cristofori's instruments, called gravicembali col piano e forte ("harpsichords with soft and loud"), were widely known throughout Europe as "pianos" (the name coming from the Italian term piano e forte).
Pianists would play at either end of an instrument like that shown in Ferdinando Cavallini's painting The Stradivarius, where a harpsichord is seen placed before two separated keyboards; one for the right hand and one for the left. Other contemporaneous depictions show a single keyboard with separate keys for each hand, e.g., in an engraving by John Mortimer, where two players are seen playing on a single instrument: one standing and using the lower keyboard and the other sitting and using the upper keyboard.
By 1727, Cristofori had built a model of the pianoforte which was better-sounding than an ordinary harpsichord. The more delicate construction allowed for greater dynamic sensitivity to perform indications like piano or pianissimo. Since its invention five years earlier, his pianofortes were becoming more popular among musicians who appreciated their ability to play soft passages at quieter volumes without sacrificing tone quality.
The piano was originally designed in the 18th century as a modification of the harpsichord, which used strings with gut or metal (bronze) cores; when metal frames replaced the "rat-hunt" method of stringing, these instruments became what we today call pianos, whether they were hammered, plucked by quills plectra, operated by pedals, etc. The name "piano e forte" is sometimes credited to Cristofori's contemporary Alessandro Scarlatti; however, the expression appeared in print only after 1732.
The difference in the sound
In a harpsichord, the jacks pluck the strings only when the player depresses a key. When you release the key, the jack immediately stops playing and rests against one of its posts until it is again pulled down to pluck another string or set of strings. On a piano, however, each hammer strikes each string immediately upon impact whether or not you hold any keys down.
Also, due to its construction involving metal rather than "wippen" style jacks that rest against their corresponding posts, even if you press all of its keys to play notes simultaneously none will be dampened by resting jacks. The result is that every note played on a piano potentially sounds until released unless something else is done to alter that or an individual note is acted upon by the player.
The traditional site of the action inside the piano is directly below the strings; this feels natural to us because that's where most stringed instruments are positioned. However, pianos don't have to be built like harpsichords. The modern upright piano, for example, puts its strings and action perpendicular to, not parallel with, its case. This frees up vertical space so that one can put pedals underneath for use in achieving certain effects (e.g., sostenuto ).
But it also means that you play with your fingers just as if you were playing a guitar-like instrument resting on your leg rather than having everything situated "upside down." Many recent digital pianos more closely resemble an unembellished upright piano than a traditional harpsichord.
You can the difference in the use of dampers. In a harpsichord, there is no way to stop notes from sounding immediately after depressing a key. Thus, when you play two notes in succession—a note and then another one an octave higher—the second note sounds while you continue to hold down the first one.
If that second note happens to be at the same pitch as one of the strings on which another key's damper has just been raised, all hell breaks loose: when that previously muted string receives sound again with no dampers left in place to prevent it, its sound echoes throughout the instrument until you lift your finger from the first key or raise its associated damper before striking the next note. This is known as "note overlap" and is one of the things that makes the harpsichord sound more percussive than melodic.
Construction and volume
There are many other differences, some of which you may find interesting. For example, on the piano, bass strings are longer than treble ones in order to produce lower notes with greater volume; moreover, each register's strings are actually made from two lengths of wire twisted together. On a harpsichord, by contrast, all strings—regardless of pitch or length—are made from a single piece of wire (metal or gut), so they don't go out of tune as readily when subjected to different humidities.
Also, unlike on an upright piano where you press down on one end to make it go up, on a modern grand piano, the part you press on is actually its lid which hinges down and lets you get at all of its strings and thus their individual pitches and overtones.
On a harpsichord, the "action," i.e., what it does when somebody plays its keys, is very different from that on a piano. On a harpsichord, each key has only one string (a fact that gives rise to tuning problems ). All notes played by depressing any given key produce sound until that note's damper silences it; if another key is depressed while one of them sounds, no sound results.
Black and white
Also, unlike in modern pianos where pressing two adjacent keys simultaneously even if they're black and white (i.e., have different pitch) is impossible, it's very easy on a harpsichord to do so—and the resulting sound produced by playing them that way can be quite beautiful.
On a modern piano, different notes are played by fundamentally different actions. For example, bass notes require one set of components between key and hammer whereas treble ones need another; hence they can't be played simultaneously any more than black and white keys could on an upright piano. This is not true for harpsichords where all their strings are hit at once with either mechanism being used for both treble and bass registers. When you play two notes on a harpsichord simultaneously, their over reinforce each other in ways that are not possible on a piano.
Moreover, the acoustical structure of harpsichords is also different from that of pianos. The action parts inside the former are visible whereas those in pianos are hidden; to play them requires very little downward pressure because their bridges (which support strings) are hinged and don't need to be depressed like those on stringed instruments like guitars or violins.
Also, unlike modern grand pianos where its soundboard's primary resonating surfaces are parallel to its plane of movement, all harpsichord soundboards have theirs perpendicular to it—again making its sound more percussive since less damping takes place than with plucked strings.
The main difference between a piano and a harpsichord is that the latter can sound more percussive because of note overlap, something impossible on the former.
All in all, this means that playing either instrument well requires radically different skills. If you wish to be proficient at both instruments, play each one exclusively for three or four years before attempting to switch between them!