Recently it has often been written that the sound of the piano cannot vary on the basis of the type of attack applied to the key, but that it depends exclusively on elements extraneous to the timbral characteristics of a single note. Naturally in the majority of cases a sound may seem "pleasant" or "ugly" depending on aspects of the performance not directly linked to the quality of a single note, but rather to the relation between the various notes. So it is worth looking more deeply into this topic. The most effective ways to influence the quality of the sound in this sense mainly concern the dynamics, the synchronization, and the pedaling.
1. The dynamics.
Timbre changes considerably when the dynamic relation between the different notes is varied: both horizontally (considering the relation of a note with the previous and following notes), and vertically (giving a different weight to each single note that makes up a chord). In this case it is clear that by piano timbre we are not referring to the sonic quality of a single note, but the result of the superimposition or succession of different notes, which gives rise to a chord or a melodic line. Every great pianist has his/her own way of dosing and combining the dynamics of the notes to obtain a given timbre, just like painters do with colors. So it is impossible sum up in just a few lines the principles that govern the combination of dynamics in a chord or in a line, but it is undoubtedly indispensable to use a wide variety of dynamics to obtain a greater wealth of timbre. For instance, if in a chord all the notes have the same dynamic, the resulting timbre will be somewhat opaque and dull. In a melodic line too, it is fundamental to vary the dynamics of each single note, other wise the phrasing will be static and lacking in inflections.
2. The synchronization.
The timbre also varies considerably depending on the synchronization of the superimposed notes: often, by playing the bass slightly before or after the melody, it is possible to enrich the cantabile effect, since by depressing the keys not perfectly at the same time a greater number of harmonics are produced. The so-called "dislocation" of notes, that is to say playing the bass before the melody, is a procedure known to all pianists, and often "forbidden" by teachers. In reality, if used appropriately, it allows a better projection of the sound, since the percussive effect of the hammers is lessened, and the independence of the various lines is better perceived. It is no mere chance that nearly all great pianists have made wide use of this device: among the most assiduous users of "dislocation", we can mention Benedetti Michelangeli, Cortot, Friedmann, and Rachmaninoff. The opposite technique can also be very effective, that is playing the melody before the bass. The delayed arrival of the bass allows a further quantity of harmonics to be developed in the strings that are already vibrating, thus obtaining a sort of extension of the dynamic curve. Many Russian pianists, including Kissin, use this procedure systematically.
3. The pedals.
a) The "una corda" pedal.
By using the left pedal, termed "una corda", it is possible to obtain not only a softening of the dynamics: a variety of degrees of timbre can also be obtained by lowering it completely or just partially. The action of the "una corda" pedal consists, in fact, of a lateral shifting of the hammer set, so that the strings are struck by a different part of the hammer. When this pedal is completely depressed, only two strings out of three are touched by the hammer, resulting in a refinement of the dynamics and timbre. But also when the pedal is only partially depressed a change in the sound is produced, because there is shift in the point of contact between the hammer and string. If the "una corda" pedal is not lowered at all, the strings are struck by a zone of the hammer that is particularly hard and compact, due to the "furrows" formed by the frequent percussion. By lowering the "una corda" pedal, the hammer is moved sideways and will touch the strings with a part that is less "beaten" (without furrows), and more elastic, thus producing a less percussive and softer sound. The effect of the "una corda" pedal is much more evident in the upper register of the instrument, but it can also be very useful in the other registers. It should not be used just for playing piano or pianissimo. It is also possible, for example, to play fortissimo with the "una corda" pedal completely depressed: in this way the sound will be more defined and incisive, but at the same time indirect and distant.
b) The sostenuto pedal
The middle pedal of a grand piano, called the sostenuto pedal, makes it possible to keep the dampers raised only on the notes played at the moment of depressing the pedal, so as to allow some strings to continue vibrating, while being able to obtain short or staccato notes with other strings. An interesting potential of this pedal is the possibility to produce harmonics: by raising the dampers of some strings, these will begin to vibrate in sympathy (without being struck by the hammer) with other strings that correspond to one of the closest harmonics. The sostenuto pedal became widespread from the second half of the 19th century, but this doesn’t exclude its effective use also when performing music written prior to this date.
c) The sustaining pedal
With regards the right pedal, named the "sustaining pedal", or simply "pedal", I recommend a very useful book by K. U. Schnabel, "Modern technique of the pedal" (Mills Music), which clearly illustrates some non conventional ways of using the pedal, for example, the vibrato or "flutter" pedal, the half pedal, the partial pedal change. Thanks to this pedal it is also possible to obtain the effects of a Forte-Piano and of a diminuendo on the same held note (by partially raising and then lowering the pedal), as well as particular types of staccato (by playing staccato with the pedal partially lowered) and of "superlegato" (changing the pedal partially, or with a slight delay). A technique frequently used is that of lowering the pedal before starting a piece: this produces a richer timbre, as many of the strings that are not struck will vibrate sympathetically. Also playing fast passages or pianissimo becomes simpler when the pedal is lowered, as the mechanics are lightened (not having to activate the dampers, which are already raised) and the action of the hammer is much easier to control and more fluid. Moreover, the "dogma" that prescribes changing the pedal whenever the harmony changes needs to be refuted. On the contrary, sometimes precisely by partially blending different harmonies one can obtain particularly beautiful timbral effects. What is more, also Beethoven, Schumann, Chopin and Liszt prescribed in their own hand the use of long pedals, with a consequent overlapping of different harmonies. A typical example of this is the third movement of Beethoven's Sonata op. 53. While taking into account that today's pianos have a greater resonance, it is still possible to respect such indications, maybe exploiting the partial pedal change. Radu Lupu is a great master of this technique.
Over and above these considerations, for each of which a whole book could be written, I nevertheless maintain that also a note considered individually, irrespective of the dynamic relations with other notes and the use of the pedals, can be varied in timbre. Basically I believe that if the same key of the same piano is played in different ways (with the same dynamic intensity and the same type of pedaling), different timbres can be obtained. That is to say, this is possible especially by working on the note after the hammer has struck.
On this matter, I would like to speak about some particular techniques that allow the vibrations of the strings to be increased or diminished.
The lengthening of the duration of the note: the "piano vibrato".
To prolong and amplify the vibration of the strings after they have been struck, it is possible to use a procedure called "piano vibrato". This is obtained by making the key partially rise and fall, after the hammer has struck the string. In this way, the hammer will return close to the strings already struck, increasing the amplitude of the vibrations thanks to the movement of the air and the shifting of the mechanics. This will result in a sound that is richer in harmonics and with a longer duration. When using this technique it is almost indispensable to keep the sustaining pedal depressed, so as to prevent the dampers, while lowering, from blocking the vibration of the strings. The frequency and amplitude of the vibrato can vary in degree, bringing about a diverse range of timbre. If the vibrato is employed for all the notes of the same chord, the result is even more evident. Of course, the use of vibrato is only possible on grand pianos, as the mechanics of vertical pianos don’t permit a good control of the movement of the hammers. Moreover, even in grand pianos, the implementation of the vibrato requires a great deal of skill and experience, as well as an optimal regulation of the mechanics, so as not to let the strings be involuntarily struck again. Pianos with the best soundboards are more sensitive to the vibrato effect. Some of the greatest pianists frequently used vibrato: the videos of Arturo Benedetti Michelangeli are a very useful testimony to this fact. The use of vibrato is fundamental to the teaching of Karl Ulrich Schnabel, one of the greatest piano teachers of the 20th century.
The shortening of the duration of the note.
On the other hand, to obtain a sound that is more incisive and percussive, it suffices to lessen the vibrations of the strings, by raising the keys partially (once or several times), so that the dampers brush the strings for an instant. This technique makes it possible to realize the diminuendo marks on long notes, which can often be found in the piano scores of Beethoven, Schubert, Schumann and Liszt. This effect can also be obtained with the aid of the pedal, as already mentioned, and can also be used to great effect together with vibrato.
I don’t dare venture into further, more speculative and not (yet) scientifically provable considerations about piano touch. Personally, though, I am convinced that a different physical approach to the keyboard can determine a different sonic result, irrespective of the dynamic intensity. What counts most, however, is the intention, that is the timbral imagination of the performer: without which, even the most efficacious technical control of the sound would prove sterile!