Pianists have used the term touch for a long time and over the years it has acquired an almost mystical connotation; a pianist is praised or condemned depending on the adjective modifier used. He may have a “singing,” “beautiful,” “pearly,” or “velvet” touch—the list is endless, depending only on the imagination of the favorably inclined critic. Conversely, if the critic is in a bad humor, the pianist’s touch may be “harsh,” “percussive,” or whatever. The worth of a pianist is measured by the quality of his touch.
Implied in all this is the belief that the pianist can in some manner control the quality of the tone he produces from the piano string by the way he strikes the key. Books have been written asserting this as fact. It has been stated categorically that if the piano key is put in motion suddenly by striking the key with the finger, the tone will be harsh and strident; conversely, if the key is gradually put in motion by being gently pressed, the tone will be smooth and mellow. If this is true, it follows that much practice would be necessary to acquire the proper manner of depressing the piano keys.
To put it bluntly, this is nonsense. In our earlier discussion of the action of the piano, we saw that at the instant the hammer strikes the string, it is completely separate from the impelling mechanism attached to the key. The speed of the hammer on striking the string depends on how the key is pressed, and determines the loudness of the resulting tone. It also determines to a certain extent the quality of the tone; a loud tone will have a greater number of higher partials than a soft tone, and so will be “brighter,” or perhaps “harsher.” A given hammer speed will thus produce a certain loudness of tone and with it a certain quality of tone, and the two are not independent; if the loudness is the same, the quality is the same. It does not matter how the hammer attained its speed, whether via a sudden acceleration by striking the key or a slower acceleration by pressing the key; a given final speed will always produce the same tone. It follows that the pianist cannot independently control the quality of the tone of a single note on the piano by the manner in which he strikes the key; a given loudness will always result in a tone of quality corresponding to that loudness.
A detailed investigation of this matter has been made in the laboratory. A mechanical striker was constructed that could depress a key of a piano and impart to it accelerations that could be varied to correspond to different ways of depressing the key with the finger. The speed of the hammer at the instant of striking the string could also be measured. The tone produced could be evaluated by recording its wave form on photographic film by means of an oscillograph. It was found that the waveform varied with the speed of the hammer; however, if the speed were kept the same, then in all cases the waveform was the same, regardless of the kind of acceleration used in striking the key. Furthermore, the waveform produced by a concert pianist striking the key could be duplicated precisely by adjusting the mechanical striker to produce the same hammer speed.
We must conclude that as far as single tones on the piano are concerned, the player does not have the ability to control quality in the manner that has been commonly assumed. The pianist himself may be subjectively convinced that he is doing so, and the adjectives applied by equally subjective critics may convince others that he is doing so. However, the objective listener will be unable to detect these supposed differences in quality by listening to individual piano tones.
Pianists as a group seem remarkably resistant to this fact, which has been pointed out to them for almost half a century.
John Backus, The Acoustical Foundations of Music, New York, 1969, pp. 246–248