The modern form of the piano, which emerged in the late 19th century, is a very different instrument from the pianos for which earlier classical piano literature was originally composed. The modern piano has a heavy metal frame, thick strings made of top-grade steel, and a sturdy action with a substantial touch weight. These changes have created a piano with a powerful tone that carries well in large halls, and which produces notes with a very long sustain time. The contrast with earlier instruments, particularly those of the 18th century (with light wooden frames, lightly sprung actions, and short sustain time) is very noticeable. These changes have given rise to interpretive questions and controversies about performing earlier literature on modern pianos, particularly since recent decades have seen the revival of historical instruments for concert use.
Background
The earliest pianos by Cristofori (ca. 1700) were lightweight objects, hardly sturdier in framing than a contemporary harpsichord, with thin strings of low tensile strength iron and brass and small, lightweight hammers. During the Classical era, when pianos first became used widely by important composers, the piano was only somewhat more robust than in Cristofori's time; see fortepiano. It was during the period from about 1790 to 1870 that most of the important changes were made that created the modern piano:
An increase in pitch range, from five octaves (see image at right) to the modern standard of seven and 1/3 octaves. iron framing, culminating in the single-piece cast iron frame ultra-tough steel strings, with three strings per note in the upper 2/3 of the instrument's range felt hammers cross-stringing in general, an enormous increase in weight and robustness. A modern Steinway Model D weighs 480 kg (990 lb), about six times the weight of a late 18th-century Stein piano. The hammers and action became much heavier so that the touch (key weight) of a modern piano is several times heavier than that of an 18th-century piano.
The prototype of the modern piano, with all of these changes in place, was exhibited to general acclaim by Steinway at the Paris exhibition of 1867; by about 1900, most leading piano manufacturers had incorporated most of these changes.
These huge changes in the piano have somewhat vexing consequences for musical performance. The problem is that much of the most widely admired piano repertoire was composed for a type of instrument that is very different from the modern instruments on which this music is normally performed today. The greatest difference is in the pianos used by the composers of the Classical era; for example, Haydn, Mozart, and Beethoven. But lesser difference are found for later composers as well. The music of the early Romantics, such as Chopin and Schumann—and even of still later composers (see below) --was written for pianos substantially different from ours.
One view that is sometimes taken is that these composers were dissatisfied with their pianos, and in fact were writing visionary "music of the future" with a more robust sound in mind. This view is perhaps plausible in the case of Beethoven, who composed at the beginning of the era of piano growth. However, many aspects of earlier music can be mentioned suggesting that it was composed very much with contemporary instruments in mind. It is these aspects that raise the greatest difficulties when a performer attempts to render earlier works on a modern instrument.
Sources of difficulty
Sustain time
The modern piano has a considerably greater sustain time than the classical-era piano. Thus, notes played in accompaniment lines will stay loud longer, and thus cover up any subsequent melodic notes more than they would have on the instrument that the composer had used. This is felt to be a particular impediment to realizing the characteristic textural clarity of Classical-era works. As an anonymous commentator (see References below) writes, "[the] earlier instruments all demonstrate a lighter and clearer sound than their modern counterparts. Lines can emerge more clearly; rapid passages and ornaments are more easily enunciated by instruments whose main purpose is not volume and power."
Pedal marks in Classical-era works
During the Classical era, the damper pedal was generally not used as it is in later music; that is, as a more or less constant amplification and modulation of the basic piano sound. Instead, pedaling was employed as a particular expressive effect, applied to certain individual musical passages.